diff --git a/backend/package.json b/backend/package.json
index 7d48806..93ebe90 100644
--- a/backend/package.json
+++ b/backend/package.json
@@ -6,7 +6,9 @@
   "scripts": {
     "start": "node src/server.js",
     "dev": "nodemon src/server.js",
-    "migrate": "node src/db/migrate.js",
+    "migrate": "node src/db/migrations-runner.js",
+    "migrate:bootstrap": "node src/db/migrations-runner.js bootstrap",
+    "migrate:legacy": "node src/db/migrate.js",
     "seed": "node src/db/seed.js",
     "seed:permissions": "node src/db/seed-permissions.js",
     "lint:routes": "node scripts/check-route-auth.js",
diff --git a/backend/src/db/migrations-runner.js b/backend/src/db/migrations-runner.js
new file mode 100644
index 0000000..52acbe6
--- /dev/null
+++ b/backend/src/db/migrations-runner.js
@@ -0,0 +1,83 @@
+'use strict';
+const fs   = require('fs');
+const path = require('path');
+const db   = require('./db');
+
+const MIGRATIONS_DIR = path.join(__dirname, 'migrations');
+
+function init() {
+  db.exec(`
+    CREATE TABLE IF NOT EXISTS _migrations (
+      filename   TEXT PRIMARY KEY,
+      applied_at TEXT NOT NULL DEFAULT (datetime('now'))
+    );
+  `);
+}
+
+function listFiles() {
+  if (!fs.existsSync(MIGRATIONS_DIR)) return [];
+  return fs.readdirSync(MIGRATIONS_DIR)
+    .filter(f => f.endsWith('.sql'))
+    .sort();
+}
+
+function applied() {
+  return new Set(db.prepare('SELECT filename FROM _migrations').all().map(r => r.filename));
+}
+
+function run() {
+  init();
+  const done    = applied();
+  const files   = listFiles();
+  const pending = files.filter(f => !done.has(f));
+
+  if (pending.length === 0) {
+    console.log('[migrate] Nothing to apply — schema is up to date');
+    return;
+  }
+
+  for (const file of pending) {
+    const sql = fs.readFileSync(path.join(MIGRATIONS_DIR, file), 'utf8');
+    console.log(`[migrate] Applying ${file}...`);
+    try {
+      db.exec('BEGIN');
+      db.exec(sql);
+      db.prepare('INSERT INTO _migrations (filename) VALUES (?)').run(file);
+      db.exec('COMMIT');
+      console.log(`[migrate] OK: ${file}`);
+    } catch (e) {
+      db.exec('ROLLBACK');
+      console.error(`[migrate] FAILED at ${file}: ${e.message}`);
+      process.exit(1);
+    }
+  }
+
+  console.log(`[migrate] Applied ${pending.length} migration(s)`);
+}
+
+/* Mark 000_baseline.sql as applied on existing DBs without running it.
+   Run once per environment after first deploy of this system. */
+function markBaseline() {
+  init();
+  const hasUsers = db.prepare("SELECT name FROM sqlite_master WHERE type='table' AND name='users'").get();
+  if (hasUsers) {
+    const done = applied();
+    if (!done.has('000_baseline.sql')) {
+      db.prepare('INSERT INTO _migrations (filename) VALUES (?)').run('000_baseline.sql');
+      console.log('[migrate] Marked 000_baseline.sql as applied (existing DB — not re-run)');
+    } else {
+      console.log('[migrate] 000_baseline.sql already marked as applied');
+    }
+  } else {
+    console.log('[migrate] No users table found — run `npm run migrate` first to initialize schema');
+    process.exit(1);
+  }
+}
+
+if (require.main === module) {
+  const cmd = process.argv[2];
+  if (cmd === 'bootstrap') markBaseline();
+  else run();
+}
+
+module.exports = { run, markBaseline };
diff --git a/backend/src/db/migrations/000_baseline.sql b/backend/src/db/migrations/000_baseline.sql
new file mode 100644
index 0000000..33bae6d
--- /dev/null
+++ b/backend/src/db/migrations/000_baseline.sql
@@ -0,0 +1,1017 @@
+CREATE TABLE achievements (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    slug        TEXT UNIQUE NOT NULL,
+    title       TEXT NOT NULL,
+    icon        TEXT NOT NULL DEFAULT '🏆',
+    category    TEXT NOT NULL DEFAULT 'general',
+    description TEXT
+  );
+
+CREATE TABLE admin_audit_log (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    admin_id   INTEGER NOT NULL REFERENCES users(id),
+    action     TEXT NOT NULL,
+    target     TEXT,
+    detail     TEXT,
+    ip         TEXT,
+    created_at TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE announcements (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    class_id   INTEGER NOT NULL REFERENCES classes(id) ON DELETE CASCADE,
+    author_id  INTEGER NOT NULL REFERENCES users(id)   ON DELETE CASCADE,
+    text       TEXT NOT NULL,
+    created_at TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE app_settings (
+    key   TEXT PRIMARY KEY,
+    value TEXT NOT NULL DEFAULT ''
+  );
+
+CREATE TABLE "assignment_sessions" (
+        id            INTEGER PRIMARY KEY AUTOINCREMENT,
+        assignment_id INTEGER NOT NULL REFERENCES assignments(id) ON DELETE CASCADE,
+        user_id       INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+        session_id    INTEGER REFERENCES test_sessions(id) ON DELETE SET NULL,
+        attempt_num   INTEGER NOT NULL DEFAULT 1,
+        first_seen_at TEXT
+      );
+
+CREATE TABLE assignment_templates (
+    id           INTEGER PRIMARY KEY AUTOINCREMENT,
+    created_by   INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    label        TEXT NOT NULL,
+    subject_slug TEXT NOT NULL,
+    mode         TEXT NOT NULL DEFAULT 'exam',
+    count        INTEGER NOT NULL DEFAULT 25,
+    topic_id     INTEGER REFERENCES topics(id) ON DELETE SET NULL,
+    test_id      INTEGER REFERENCES tests(id)  ON DELETE SET NULL,
+    file_id      INTEGER REFERENCES files(id)  ON DELETE SET NULL,
+    is_homework  INTEGER NOT NULL DEFAULT 0,
+    created_at   TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE "assignments" (
+        id           INTEGER PRIMARY KEY AUTOINCREMENT,
+        class_id     INTEGER REFERENCES classes(id) ON DELETE CASCADE,
+        user_id      INTEGER REFERENCES users(id)   ON DELETE CASCADE,
+        title        TEXT NOT NULL,
+        subject_slug TEXT NOT NULL,
+        mode         TEXT NOT NULL DEFAULT 'exam',
+        count        INTEGER NOT NULL DEFAULT 25,
+        topic_id     INTEGER REFERENCES topics(id) ON DELETE SET NULL,
+        deadline     TEXT,
+        created_by   INTEGER NOT NULL REFERENCES users(id),
+        test_id      INTEGER REFERENCES tests(id) ON DELETE SET NULL,
+        created_at   TEXT NOT NULL DEFAULT (datetime('now'))
+      , file_id INTEGER REFERENCES files(id) ON DELETE SET NULL, is_homework INTEGER NOT NULL DEFAULT 0, max_attempts INTEGER NOT NULL DEFAULT 0);
+
+CREATE TABLE avatar_requests (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id     INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    filename    TEXT    NOT NULL,
+    status      TEXT    NOT NULL DEFAULT 'pending',
+    reviewer_id INTEGER REFERENCES users(id),
+    reject_msg  TEXT,
+    created_at  TEXT    NOT NULL DEFAULT (datetime('now')),
+    reviewed_at TEXT
+  );
+
+CREATE TABLE bio_challenges (
+    id             INTEGER PRIMARY KEY AUTOINCREMENT,
+    title          TEXT NOT NULL,
+    description    TEXT NOT NULL DEFAULT '',
+    type           TEXT NOT NULL DEFAULT 'build',
+    target_formula TEXT NOT NULL DEFAULT '',
+    hint           TEXT DEFAULT NULL,
+    xp_reward      INTEGER NOT NULL DEFAULT 50,
+    difficulty     INTEGER NOT NULL DEFAULT 1,
+    topic_tag      TEXT DEFAULT NULL,
+    order_n        INTEGER NOT NULL DEFAULT 0
+  , data_json TEXT DEFAULT NULL);
+
+CREATE TABLE bio_elements (
+    symbol       TEXT PRIMARY KEY,
+    name_ru      TEXT NOT NULL,
+    valency_max  INTEGER NOT NULL DEFAULT 1,
+    valency_opts TEXT NOT NULL DEFAULT '[1]',
+    color        TEXT NOT NULL DEFAULT '#888888',
+    radius       INTEGER NOT NULL DEFAULT 20,
+    mass         REAL NOT NULL DEFAULT 1.0
+  );
+
+CREATE TABLE bio_molecules (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    formula     TEXT NOT NULL,
+    name_ru     TEXT NOT NULL,
+    name_lat    TEXT NOT NULL DEFAULT '',
+    category    TEXT NOT NULL DEFAULT 'inorganic',
+    difficulty  INTEGER NOT NULL DEFAULT 1,
+    description TEXT NOT NULL DEFAULT '',
+    atoms_json  TEXT NOT NULL DEFAULT '[]',
+    bonds_json  TEXT NOT NULL DEFAULT '[]',
+    is_library  INTEGER NOT NULL DEFAULT 1,
+    topic_tags  TEXT NOT NULL DEFAULT '[]',
+    created_at  TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE bio_reactions (
+    id           INTEGER PRIMARY KEY AUTOINCREMENT,
+    equation     TEXT NOT NULL,
+    name_ru      TEXT NOT NULL,
+    type         TEXT NOT NULL DEFAULT 'synthesis',
+    description  TEXT NOT NULL DEFAULT '',
+    reactant_ids TEXT NOT NULL DEFAULT '[]',
+    product_ids  TEXT NOT NULL DEFAULT '[]',
+    conditions   TEXT DEFAULT NULL,
+    energy_kj    REAL DEFAULT NULL,
+    topic_tags   TEXT NOT NULL DEFAULT '[]'
+  );
+
+CREATE TABLE bio_user_challenges (
+    user_id      INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    challenge_id INTEGER NOT NULL REFERENCES bio_challenges(id) ON DELETE CASCADE,
+    completed_at TEXT NOT NULL DEFAULT (datetime('now')),
+    PRIMARY KEY (user_id, challenge_id)
+  );
+
+CREATE TABLE bio_user_molecules (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id     INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    molecule_id INTEGER REFERENCES bio_molecules(id),
+    name        TEXT DEFAULT NULL,
+    formula     TEXT NOT NULL,
+    atoms_json  TEXT NOT NULL,
+    bonds_json  TEXT NOT NULL,
+    created_at  TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE bookmarks (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id     INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    entity_type TEXT NOT NULL CHECK (entity_type IN ('lesson','course','file','question')),
+    entity_id   INTEGER NOT NULL,
+    created_at  TEXT NOT NULL DEFAULT (datetime('now')),
+    UNIQUE (user_id, entity_type, entity_id)
+  );
+
+CREATE TABLE challenges (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id     INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    week        TEXT NOT NULL,
+    title       TEXT NOT NULL,
+    description TEXT,
+    type        TEXT NOT NULL DEFAULT 'tests',
+    target      INTEGER NOT NULL DEFAULT 3,
+    progress    INTEGER NOT NULL DEFAULT 0,
+    xp_reward   INTEGER NOT NULL DEFAULT 100,
+    subject_slug TEXT,
+    topic_id    INTEGER,
+    completed   INTEGER NOT NULL DEFAULT 0,
+    claimed     INTEGER NOT NULL DEFAULT 0,
+    UNIQUE(user_id, week, title)
+  );
+
+CREATE TABLE class_courses (
+    class_id    INTEGER NOT NULL REFERENCES classes(id)  ON DELETE CASCADE,
+    course_id   INTEGER NOT NULL REFERENCES courses(id)  ON DELETE CASCADE,
+    deadline    TEXT,
+    assigned_by INTEGER REFERENCES users(id) ON DELETE SET NULL,
+    assigned_at TEXT NOT NULL DEFAULT (datetime('now')),
+    PRIMARY KEY (class_id, course_id)
+  );
+
+CREATE TABLE class_members (
+    id        INTEGER PRIMARY KEY AUTOINCREMENT,
+    class_id  INTEGER NOT NULL REFERENCES classes(id) ON DELETE CASCADE,
+    user_id   INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    joined_at TEXT NOT NULL DEFAULT (datetime('now')),
+    UNIQUE (class_id, user_id)
+  );
+
+CREATE TABLE classes (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    name        TEXT NOT NULL,
+    description TEXT,
+    teacher_id  INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    invite_code TEXT UNIQUE NOT NULL,
+    created_at  TEXT NOT NULL DEFAULT (datetime('now'))
+  , features TEXT, cover_emoji TEXT NOT NULL DEFAULT '');
+
+CREATE TABLE classroom_attendance (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    session_id INTEGER NOT NULL REFERENCES classroom_sessions(id) ON DELETE CASCADE,
+    user_id    INTEGER NOT NULL REFERENCES users(id),
+    joined_at  TEXT NOT NULL DEFAULT (datetime('now')),
+    left_at    TEXT,
+    UNIQUE(session_id, user_id)
+  );
+
+CREATE TABLE classroom_chat (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    session_id INTEGER NOT NULL REFERENCES classroom_sessions(id) ON DELETE CASCADE,
+    user_id    INTEGER NOT NULL REFERENCES users(id),
+    message    TEXT NOT NULL,
+    created_at TEXT NOT NULL DEFAULT (datetime('now'))
+  , pinned INTEGER NOT NULL DEFAULT 0, attachment_url  TEXT, attachment_type TEXT);
+
+CREATE TABLE classroom_chat_reactions (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    chat_id    INTEGER NOT NULL REFERENCES classroom_chat(id) ON DELETE CASCADE,
+    user_id    INTEGER NOT NULL REFERENCES users(id),
+    reaction   TEXT    NOT NULL,
+    created_at TEXT    NOT NULL DEFAULT (datetime('now')),
+    UNIQUE(chat_id, user_id, reaction)
+  );
+
+CREATE TABLE classroom_draw_permissions (
+    session_id INTEGER NOT NULL REFERENCES classroom_sessions(id) ON DELETE CASCADE,
+    user_id    INTEGER NOT NULL REFERENCES users(id),
+    PRIMARY KEY (session_id, user_id)
+  );
+
+CREATE TABLE classroom_hands (
+    session_id INTEGER NOT NULL REFERENCES classroom_sessions(id) ON DELETE CASCADE,
+    user_id    INTEGER NOT NULL REFERENCES users(id),
+    PRIMARY KEY (session_id, user_id)
+  );
+
+CREATE TABLE classroom_invites (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    session_id INTEGER NOT NULL REFERENCES classroom_sessions(id) ON DELETE CASCADE,
+    user_id    INTEGER NOT NULL REFERENCES users(id),
+    UNIQUE(session_id, user_id)
+  );
+
+CREATE TABLE classroom_notes (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    session_id INTEGER NOT NULL REFERENCES classroom_sessions(id) ON DELETE CASCADE,
+    user_id    INTEGER NOT NULL REFERENCES users(id),
+    content    TEXT    NOT NULL DEFAULT '',
+    updated_at TEXT    NOT NULL DEFAULT (datetime('now')),
+    UNIQUE(session_id, user_id)
+  );
+
+CREATE TABLE classroom_pages (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    session_id INTEGER NOT NULL REFERENCES classroom_sessions(id) ON DELETE CASCADE,
+    page_num   INTEGER NOT NULL DEFAULT 1,
+    bg_color   TEXT NOT NULL DEFAULT '#ffffff', template TEXT NOT NULL DEFAULT 'blank', name TEXT,
+    UNIQUE(session_id, page_num)
+  );
+
+CREATE TABLE classroom_sessions (
+    id           INTEGER PRIMARY KEY AUTOINCREMENT,
+    class_id     INTEGER REFERENCES classes(id) ON DELETE CASCADE,
+    teacher_id   INTEGER NOT NULL REFERENCES users(id),
+    title        TEXT NOT NULL DEFAULT '',
+    status       TEXT NOT NULL DEFAULT 'active',
+    current_page INTEGER NOT NULL DEFAULT 1,
+    created_at   TEXT NOT NULL DEFAULT (datetime('now')),
+    ended_at     TEXT
+  , board_theme TEXT NOT NULL DEFAULT 'chalkboard');
+
+CREATE TABLE classroom_strokes (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    session_id INTEGER NOT NULL REFERENCES classroom_sessions(id) ON DELETE CASCADE,
+    page_num   INTEGER NOT NULL DEFAULT 1,
+    user_id    INTEGER NOT NULL REFERENCES users(id),
+    tool       TEXT NOT NULL DEFAULT 'pencil',
+    data       TEXT NOT NULL,
+    seq        INTEGER NOT NULL,
+    created_at TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE classroom_templates (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    teacher_id  INTEGER NOT NULL REFERENCES users(id),
+    title       TEXT    NOT NULL,
+    description TEXT    DEFAULT '',
+    pages_data  TEXT    NOT NULL DEFAULT '[]',
+    created_at  TEXT    NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE course_sections (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    course_id   INTEGER NOT NULL REFERENCES courses(id) ON DELETE CASCADE,
+    title       TEXT NOT NULL,
+    order_index INTEGER NOT NULL DEFAULT 0
+  );
+
+CREATE TABLE course_templates (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    title       TEXT NOT NULL,
+    description TEXT,
+    category    TEXT NOT NULL DEFAULT 'general',
+    subject_slug TEXT,
+    structure   TEXT NOT NULL DEFAULT '{}',
+    is_public   INTEGER NOT NULL DEFAULT 0,
+    created_by  INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    created_at  TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE courses (
+    id           INTEGER PRIMARY KEY AUTOINCREMENT,
+    subject_slug TEXT NOT NULL,
+    title        TEXT NOT NULL,
+    description  TEXT,
+    cover_emoji  TEXT NOT NULL DEFAULT '📚',
+    order_index  INTEGER NOT NULL DEFAULT 0,
+    is_published INTEGER NOT NULL DEFAULT 0,
+    created_by   INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    created_at   TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE daily_goals (
+    id           INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id      INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    date         TEXT NOT NULL,
+    tests_target INTEGER NOT NULL DEFAULT 3,
+    tests_done   INTEGER NOT NULL DEFAULT 0,
+    xp_target    INTEGER NOT NULL DEFAULT 200,
+    xp_earned    INTEGER NOT NULL DEFAULT 0,
+    UNIQUE (user_id, date)
+  );
+
+CREATE TABLE error_log (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    level      TEXT NOT NULL DEFAULT 'error',
+    message    TEXT NOT NULL,
+    stack      TEXT,
+    route      TEXT,
+    method     TEXT,
+    user_id    INTEGER,
+    created_at TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE file_access (
+    id        INTEGER PRIMARY KEY AUTOINCREMENT,
+    file_id   INTEGER NOT NULL REFERENCES files(id) ON DELETE CASCADE,
+    type      TEXT NOT NULL CHECK (type IN ('class', 'user')),
+    target_id INTEGER NOT NULL,
+    UNIQUE (file_id, type, target_id)
+  );
+
+CREATE TABLE files (
+    id            INTEGER PRIMARY KEY AUTOINCREMENT,
+    title         TEXT NOT NULL,
+    description   TEXT,
+    original_name TEXT NOT NULL,
+    stored_name   TEXT NOT NULL UNIQUE,
+    mimetype      TEXT,
+    size          INTEGER,
+    subject_slug  TEXT,
+    is_public     INTEGER NOT NULL DEFAULT 1,
+    uploaded_by   INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    created_at    TEXT NOT NULL DEFAULT (datetime('now'))
+  , folder_id INTEGER);
+
+CREATE TABLE flashcard_cards (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    deck_id    INTEGER NOT NULL REFERENCES flashcard_decks(id) ON DELETE CASCADE,
+    front      TEXT NOT NULL DEFAULT '',
+    back       TEXT NOT NULL DEFAULT '',
+    order_idx  INTEGER NOT NULL DEFAULT 0,
+    created_at TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE flashcard_decks (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id     INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    title       TEXT NOT NULL,
+    description TEXT NOT NULL DEFAULT '',
+    color       TEXT NOT NULL DEFAULT '#9B5DE5',
+    created_at  TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE flashcard_reviews (
+    id            INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id       INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    card_id       INTEGER NOT NULL REFERENCES flashcard_cards(id) ON DELETE CASCADE,
+    ease_factor   REAL NOT NULL DEFAULT 2.5,
+    interval_days INTEGER NOT NULL DEFAULT 1,
+    repetitions   INTEGER NOT NULL DEFAULT 0,
+    due_at        TEXT NOT NULL DEFAULT (datetime('now')),
+    last_reviewed TEXT,
+    UNIQUE(user_id, card_id)
+  );
+
+CREATE TABLE folder_access (
+    id        INTEGER PRIMARY KEY AUTOINCREMENT,
+    folder_id INTEGER NOT NULL REFERENCES folders(id) ON DELETE CASCADE,
+    type      TEXT NOT NULL CHECK (type IN ('class', 'user')),
+    target_id INTEGER NOT NULL,
+    UNIQUE (folder_id, type, target_id)
+  );
+
+CREATE TABLE folders (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    name       TEXT NOT NULL,
+    created_by INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    created_at TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE geometry_submissions (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    task_id     INTEGER NOT NULL REFERENCES geometry_tasks(id) ON DELETE CASCADE,
+    student_id  INTEGER NOT NULL REFERENCES users(id),
+    state_json  TEXT    NOT NULL DEFAULT '{}',
+    score       REAL    DEFAULT NULL,
+    feedback    TEXT    DEFAULT '',
+    submitted_at TEXT   NOT NULL DEFAULT (datetime('now')),
+    UNIQUE(task_id, student_id)
+  );
+
+CREATE TABLE geometry_tasks (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    teacher_id  INTEGER NOT NULL REFERENCES users(id),
+    class_id    INTEGER REFERENCES classes(id) ON DELETE SET NULL,
+    title       TEXT    NOT NULL DEFAULT 'Без названия',
+    description TEXT    DEFAULT '',
+    state_json  TEXT    NOT NULL DEFAULT '{}',
+    created_at  TEXT    NOT NULL DEFAULT (datetime('now')),
+    updated_at  TEXT    NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE "lesson_blocks" (
+      id          INTEGER PRIMARY KEY AUTOINCREMENT,
+      lesson_id   INTEGER NOT NULL REFERENCES lessons(id) ON DELETE CASCADE,
+      type        TEXT NOT NULL DEFAULT 'text'
+                  CHECK (type IN ('heading','text','formula','image','quiz','sim',
+                                  'table','code','divider','callout','video','flashcard',
+                                  'matching','fill-blank','ordering',
+                                  'accordion','timeline','diagram','geogebra','audio','columns','alert')),
+      order_index INTEGER NOT NULL DEFAULT 0,
+      data        TEXT NOT NULL DEFAULT '{}'
+    );
+
+CREATE TABLE lesson_comments (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    lesson_id  INTEGER NOT NULL REFERENCES lessons(id) ON DELETE CASCADE,
+    user_id    INTEGER NOT NULL REFERENCES users(id)   ON DELETE CASCADE,
+    parent_id  INTEGER REFERENCES lesson_comments(id)  ON DELETE CASCADE,
+    text       TEXT NOT NULL,
+    created_at TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE lesson_notes (
+    user_id     INTEGER NOT NULL REFERENCES users(id)   ON DELETE CASCADE,
+    lesson_id   INTEGER NOT NULL REFERENCES lessons(id) ON DELETE CASCADE,
+    text        TEXT NOT NULL DEFAULT '',
+    updated_at  TEXT NOT NULL DEFAULT (datetime('now')),
+    PRIMARY KEY (user_id, lesson_id)
+  );
+
+CREATE TABLE lesson_progress (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id     INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    lesson_id   INTEGER NOT NULL REFERENCES lessons(id) ON DELETE CASCADE,
+    completed   INTEGER NOT NULL DEFAULT 0,
+    updated_at  TEXT NOT NULL DEFAULT (datetime('now')),
+    UNIQUE (user_id, lesson_id)
+  );
+
+CREATE TABLE lesson_templates (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    title       TEXT NOT NULL,
+    category    TEXT NOT NULL DEFAULT 'general',
+    subject_slug TEXT,
+    blocks      TEXT NOT NULL DEFAULT '[]',
+    is_public   INTEGER NOT NULL DEFAULT 0,
+    created_by  INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    created_at  TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE lessons (
+    id           INTEGER PRIMARY KEY AUTOINCREMENT,
+    course_id    INTEGER NOT NULL REFERENCES courses(id) ON DELETE CASCADE,
+    title        TEXT NOT NULL,
+    order_index  INTEGER NOT NULL DEFAULT 0,
+    is_published INTEGER NOT NULL DEFAULT 0,
+    created_at   TEXT NOT NULL DEFAULT (datetime('now'))
+  , section_id INTEGER REFERENCES course_sections(id) ON DELETE SET NULL, read_time  INTEGER NOT NULL DEFAULT 0);
+
+CREATE TABLE "live_answers" (
+        id               INTEGER PRIMARY KEY AUTOINCREMENT,
+        live_session_id  INTEGER NOT NULL REFERENCES live_sessions(id) ON DELETE CASCADE,
+        user_id          INTEGER NOT NULL REFERENCES users(id),
+        question_id      INTEGER REFERENCES questions(id) ON DELETE SET NULL,
+        option_id        INTEGER REFERENCES options(id),
+        answer_text      TEXT,
+        is_correct       INTEGER,
+        answered_at      TEXT NOT NULL DEFAULT (datetime('now')),
+        UNIQUE(live_session_id, user_id, question_id)
+      );
+
+CREATE TABLE live_sessions (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    class_id    INTEGER NOT NULL REFERENCES classes(id)    ON DELETE CASCADE,
+    teacher_id  INTEGER NOT NULL REFERENCES users(id),
+    question_id INTEGER          REFERENCES questions(id),
+    status      TEXT    NOT NULL DEFAULT 'waiting',
+    show_results INTEGER NOT NULL DEFAULT 0,
+    created_at  TEXT    NOT NULL DEFAULT (datetime('now')),
+    ended_at    TEXT
+  );
+
+CREATE TABLE notifications (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id    INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    type       TEXT NOT NULL DEFAULT 'info',
+    message    TEXT NOT NULL,
+    link       TEXT,
+    is_read    INTEGER NOT NULL DEFAULT 0,
+    created_at TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE options (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    question_id INTEGER NOT NULL REFERENCES questions(id) ON DELETE CASCADE,
+    text        TEXT NOT NULL,
+    is_correct  INTEGER NOT NULL DEFAULT 0,
+    order_index INTEGER NOT NULL DEFAULT 0
+  , match_pair TEXT);
+
+CREATE TABLE parent_links (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    student_id  INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    token       TEXT UNIQUE NOT NULL,
+    label       TEXT NOT NULL DEFAULT '',
+    is_active   INTEGER NOT NULL DEFAULT 1,
+    last_used   TEXT,
+    created_at  TEXT NOT NULL DEFAULT (datetime('now')),
+    expires_at  TEXT
+  );
+
+CREATE TABLE parent_notifications (
+    id             INTEGER PRIMARY KEY AUTOINCREMENT,
+    parent_link_id INTEGER NOT NULL REFERENCES parent_links(id) ON DELETE CASCADE,
+    type           TEXT NOT NULL DEFAULT 'info',
+    message        TEXT NOT NULL,
+    is_read        INTEGER NOT NULL DEFAULT 0,
+    created_at     TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE questions (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    subject_id  INTEGER NOT NULL REFERENCES subjects(id) ON DELETE CASCADE,
+    topic_id    INTEGER REFERENCES topics(id) ON DELETE SET NULL,
+    text        TEXT NOT NULL,
+    difficulty  INTEGER NOT NULL DEFAULT 1 CHECK (difficulty BETWEEN 1 AND 3),
+    year        INTEGER,
+    explanation TEXT,
+    created_at  TEXT NOT NULL DEFAULT (datetime('now'))
+  , type TEXT NOT NULL DEFAULT 'single', correct_text TEXT, image TEXT, source_type TEXT NOT NULL DEFAULT 'базовый');
+
+CREATE TABLE rb_food_web (
+    predator_id INTEGER NOT NULL REFERENCES rb_species(id) ON DELETE CASCADE,
+    prey_id     INTEGER NOT NULL REFERENCES rb_species(id) ON DELETE CASCADE,
+    strength    REAL    NOT NULL DEFAULT 0.5,
+    PRIMARY KEY (predator_id, prey_id)
+  );
+
+CREATE TABLE rb_groups (
+    id       INTEGER PRIMARY KEY AUTOINCREMENT,
+    name_ru  TEXT NOT NULL,
+    name_lat TEXT NOT NULL DEFAULT '',
+    icon     TEXT NOT NULL DEFAULT '🌿',
+    color    TEXT NOT NULL DEFAULT '#16a34a'
+  );
+
+CREATE TABLE rb_habitats (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    name        TEXT NOT NULL,
+    type        TEXT NOT NULL DEFAULT 'forest',
+    description TEXT NOT NULL DEFAULT '',
+    sound_file  TEXT NOT NULL DEFAULT ''
+  );
+
+CREATE TABLE rb_population_data (
+    id             INTEGER PRIMARY KEY AUTOINCREMENT,
+    species_id     INTEGER NOT NULL REFERENCES rb_species(id) ON DELETE CASCADE,
+    year           INTEGER NOT NULL,
+    count_estimate INTEGER NOT NULL DEFAULT 0,
+    source         TEXT    NOT NULL DEFAULT ''
+  );
+
+CREATE TABLE rb_quests (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    title       TEXT    NOT NULL,
+    description TEXT    NOT NULL DEFAULT '',
+    species_ids TEXT    NOT NULL DEFAULT '[]',
+    xp_reward   INTEGER NOT NULL DEFAULT 150,
+    badge_slug  TEXT    NOT NULL DEFAULT ''
+  );
+
+CREATE TABLE rb_sightings (
+    id                  INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id             INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    species_id          INTEGER NOT NULL REFERENCES rb_species(id) ON DELETE CASCADE,
+    region_code         TEXT    NOT NULL DEFAULT '',
+    description         TEXT    NOT NULL DEFAULT '',
+    photo_url           TEXT    NOT NULL DEFAULT '',
+    confirmed_by_teacher INTEGER NOT NULL DEFAULT 0,
+    created_at          TEXT    NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE rb_species (
+    id                  INTEGER PRIMARY KEY AUTOINCREMENT,
+    group_id            INTEGER NOT NULL REFERENCES rb_groups(id),
+    habitat_id          INTEGER REFERENCES rb_habitats(id),
+    name_ru             TEXT NOT NULL,
+    name_be             TEXT NOT NULL DEFAULT '',
+    name_lat            TEXT NOT NULL DEFAULT '',
+    category            TEXT NOT NULL DEFAULT 'VU'
+                        CHECK (category IN ('CR','EN','VU','NT','LC')),
+    by_category         TEXT NOT NULL DEFAULT 'III',
+    description         TEXT NOT NULL DEFAULT '',
+    interesting_fact    TEXT NOT NULL DEFAULT '',
+    threats             TEXT NOT NULL DEFAULT '[]',
+    conservation        TEXT NOT NULL DEFAULT '',
+    where_to_see        TEXT NOT NULL DEFAULT '',
+    photo_url           TEXT NOT NULL DEFAULT '',
+    model_type          TEXT NOT NULL DEFAULT 'silhouette'
+                        CHECK (model_type IN ('procedural','silhouette','none')),
+    population_trend    TEXT NOT NULL DEFAULT '[]',
+    biomass_kg          REAL NOT NULL DEFAULT 0,
+    created_at          TEXT NOT NULL DEFAULT (datetime('now'))
+  , season_active TEXT NOT NULL DEFAULT '', name_be_short TEXT NOT NULL DEFAULT '');
+
+CREATE TABLE rb_species_regions (
+    species_id  INTEGER NOT NULL REFERENCES rb_species(id) ON DELETE CASCADE,
+    region_code TEXT NOT NULL
+                CHECK (region_code IN ('brest','vitebsk','gomel','grodno','minsk','mogilev')),
+    PRIMARY KEY (species_id, region_code)
+  );
+
+CREATE TABLE rb_user_collection (
+    user_id       INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    species_id    INTEGER NOT NULL REFERENCES rb_species(id) ON DELETE CASCADE,
+    unlock_method TEXT    NOT NULL DEFAULT 'explore',
+    notes         TEXT    NOT NULL DEFAULT '',
+    unlocked_at   TEXT    NOT NULL DEFAULT (datetime('now')),
+    PRIMARY KEY (user_id, species_id)
+  );
+
+CREATE TABLE rb_user_quests (
+    user_id      INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    quest_id     INTEGER NOT NULL REFERENCES rb_quests(id) ON DELETE CASCADE,
+    status       TEXT    NOT NULL DEFAULT 'active'
+                 CHECK (status IN ('active','completed')),
+    progress     TEXT    NOT NULL DEFAULT '{}',
+    completed_at TEXT,
+    PRIMARY KEY (user_id, quest_id)
+  );
+
+CREATE TABLE "role_permissions" (
+      id         INTEGER PRIMARY KEY AUTOINCREMENT,
+      role       TEXT NOT NULL CHECK (role IN ('teacher', 'student', 'free_student')),
+      permission TEXT NOT NULL,
+      enabled    INTEGER NOT NULL DEFAULT 0,
+      UNIQUE (role, permission)
+    );
+
+CREATE TABLE session_questions (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    session_id  INTEGER NOT NULL REFERENCES test_sessions(id) ON DELETE CASCADE,
+    question_id INTEGER NOT NULL REFERENCES questions(id),
+    order_index INTEGER NOT NULL
+  );
+
+CREATE TABLE shop_items (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    name        TEXT NOT NULL,
+    description TEXT,
+    type        TEXT NOT NULL DEFAULT 'frame'
+                CHECK (type IN ('frame','theme','title','effect')),
+    category    TEXT NOT NULL DEFAULT 'cosmetic',
+    price       INTEGER NOT NULL DEFAULT 100,
+    data        TEXT NOT NULL DEFAULT '{}',
+    icon        TEXT NOT NULL DEFAULT 'star',
+    is_active   INTEGER NOT NULL DEFAULT 1,
+    created_at  TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE subjects (
+    id   INTEGER PRIMARY KEY AUTOINCREMENT,
+    slug TEXT UNIQUE NOT NULL,
+    name TEXT NOT NULL,
+    icon TEXT
+  , default_mode  TEXT NOT NULL DEFAULT 'exam', default_count INTEGER NOT NULL DEFAULT 25, default_test_id INTEGER REFERENCES tests(id) ON DELETE SET NULL);
+
+CREATE TABLE submission_log (
+    id              INTEGER PRIMARY KEY AUTOINCREMENT,
+    submission_id   INTEGER NOT NULL,
+    class_id        INTEGER,
+    assignment_id   INTEGER,
+    student_id      INTEGER NOT NULL,
+    student_name    TEXT,
+    original_name   TEXT,
+    status          TEXT,
+    grade           INTEGER,
+    teacher_note    TEXT,
+    submitted_at    TEXT,
+    action          TEXT NOT NULL DEFAULT 'deleted',
+    deleted_by      INTEGER NOT NULL,
+    deleted_by_role TEXT,
+    deleted_at      TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE "submissions" (
+      id            INTEGER PRIMARY KEY AUTOINCREMENT,
+      class_id      INTEGER NOT NULL REFERENCES classes(id) ON DELETE CASCADE,
+      assignment_id INTEGER REFERENCES assignments(id) ON DELETE SET NULL,
+      student_id    INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+      original_name TEXT NOT NULL,
+      stored_name   TEXT NOT NULL UNIQUE,
+      mimetype      TEXT,
+      size          INTEGER,
+      message       TEXT,
+      status        TEXT NOT NULL DEFAULT 'new' CHECK (status IN ('new','reviewed','revision','resubmitted','accepted')),
+      teacher_note  TEXT,
+      grade         INTEGER,
+      reviewed_at   TEXT,
+      submitted_at  TEXT NOT NULL DEFAULT (datetime('now'))
+    );
+
+CREATE TABLE test_questions (
+    test_id      INTEGER NOT NULL REFERENCES tests(id) ON DELETE CASCADE,
+    question_id  INTEGER NOT NULL REFERENCES questions(id) ON DELETE CASCADE,
+    order_index  INTEGER NOT NULL DEFAULT 0,
+    PRIMARY KEY (test_id, question_id)
+  );
+
+CREATE TABLE test_sessions (
+    id           INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id      INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    subject_id   INTEGER REFERENCES subjects(id) ON DELETE SET NULL,
+    mode         TEXT NOT NULL DEFAULT 'exam'
+                 CHECK (mode IN ('exam', 'practice', 'topic', 'random')),
+    total        INTEGER NOT NULL,
+    score        INTEGER,
+    status       TEXT NOT NULL DEFAULT 'in_progress'
+                 CHECK (status IN ('in_progress', 'completed', 'abandoned')),
+    started_at   TEXT NOT NULL DEFAULT (datetime('now')),
+    finished_at  TEXT
+  );
+
+CREATE TABLE tests (
+    id           INTEGER PRIMARY KEY AUTOINCREMENT,
+    title        TEXT NOT NULL,
+    subject_slug TEXT NOT NULL,
+    description  TEXT,
+    created_by   INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    created_at   TEXT NOT NULL DEFAULT (datetime('now'))
+  , show_answers INTEGER NOT NULL DEFAULT 1, time_limit INTEGER);
+
+CREATE TABLE topics (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    subject_id  INTEGER NOT NULL REFERENCES subjects(id) ON DELETE CASCADE,
+    name        TEXT NOT NULL,
+    order_index INTEGER NOT NULL DEFAULT 0
+  );
+
+CREATE TABLE user_achievements (
+    id             INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id        INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    achievement_id INTEGER NOT NULL REFERENCES achievements(id) ON DELETE CASCADE,
+    unlocked_at    TEXT NOT NULL DEFAULT (datetime('now')),
+    UNIQUE (user_id, achievement_id)
+  );
+
+CREATE TABLE user_answers (
+    id               INTEGER PRIMARY KEY AUTOINCREMENT,
+    session_id       INTEGER NOT NULL REFERENCES test_sessions(id) ON DELETE CASCADE,
+    question_id      INTEGER NOT NULL REFERENCES questions(id),
+    chosen_option_id INTEGER REFERENCES options(id),
+    is_correct       INTEGER,
+    time_spent_sec   INTEGER,
+    answered_at      TEXT NOT NULL DEFAULT (datetime('now')), answer_text TEXT,
+    UNIQUE (session_id, question_id)
+  );
+
+CREATE TABLE user_permissions (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id    INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    permission TEXT NOT NULL,
+    enabled    INTEGER NOT NULL DEFAULT 0,
+    UNIQUE (user_id, permission)
+  );
+
+CREATE TABLE user_preferences (
+    user_id    INTEGER PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
+    data       TEXT    NOT NULL DEFAULT '{}',
+    updated_at TEXT    NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE TABLE user_purchases (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id     INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    item_id     INTEGER NOT NULL REFERENCES shop_items(id) ON DELETE CASCADE,
+    purchased_at TEXT NOT NULL DEFAULT (datetime('now')),
+    UNIQUE(user_id, item_id)
+  );
+
+CREATE TABLE "users" (
+        id              INTEGER PRIMARY KEY AUTOINCREMENT,
+        email           TEXT UNIQUE NOT NULL,
+        password_hash   TEXT NOT NULL,
+        name            TEXT NOT NULL,
+        role            TEXT NOT NULL DEFAULT 'student'
+                        CHECK (role IN ('student','teacher','admin','free_student')),
+        created_at      TEXT NOT NULL DEFAULT (datetime('now')),
+        last_login      TEXT,
+        xp              INTEGER NOT NULL DEFAULT 0,
+        level           INTEGER NOT NULL DEFAULT 1,
+        streak_current  INTEGER NOT NULL DEFAULT 0,
+        streak_best     INTEGER NOT NULL DEFAULT 0,
+        streak_date     TEXT,
+        goal_tier       TEXT DEFAULT 'medium',
+        avatar_frame    TEXT DEFAULT 'default',
+        coins           INTEGER NOT NULL DEFAULT 0,
+        active_title    TEXT DEFAULT NULL,
+        active_theme    TEXT DEFAULT NULL,
+        active_effect   TEXT DEFAULT NULL,
+        token_version   INTEGER NOT NULL DEFAULT 0,
+        lab_experiments INTEGER NOT NULL DEFAULT 0,
+        lab_reactions   INTEGER NOT NULL DEFAULT 0,
+        is_banned       INTEGER NOT NULL DEFAULT 0
+      , pet_name TEXT, pet_color TEXT DEFAULT 'purple', pet_last_petted TEXT, pet_petting_streak INT DEFAULT 0, pet_last_star TEXT, pet_bg TEXT DEFAULT 'default', pet_bg_owned TEXT DEFAULT '[]', pet_last_fed TEXT, avatar_url TEXT DEFAULT NULL);
+
+CREATE TABLE xp_log (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id    INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    amount     INTEGER NOT NULL,
+    reason     TEXT NOT NULL,
+    created_at TEXT NOT NULL DEFAULT (datetime('now'))
+  );
+
+CREATE INDEX idx_announcements_class ON announcements(class_id);
+
+CREATE INDEX idx_answers_session   ON user_answers(session_id);
+
+CREATE INDEX idx_answers_sq           ON user_answers(session_id, question_id);
+
+CREATE INDEX idx_assign_sess_assign ON assignment_sessions(assignment_id);
+
+CREATE INDEX idx_assign_sess_user   ON assignment_sessions(user_id);
+
+CREATE INDEX idx_assignments_class ON assignments(class_id);
+
+CREATE INDEX idx_assignments_deadline      ON assignments(deadline);
+
+CREATE INDEX idx_assignments_user  ON assignments(user_id);
+
+CREATE INDEX idx_audit_log_admin ON admin_audit_log(admin_id);
+
+CREATE INDEX idx_audit_log_date ON admin_audit_log(created_at DESC);
+
+CREATE INDEX idx_avatar_req_status ON avatar_requests(status);
+
+CREATE INDEX idx_avatar_req_user   ON avatar_requests(user_id);
+
+CREATE INDEX idx_bio_mol_cat     ON bio_molecules(category);
+
+CREATE INDEX idx_bio_mol_formula ON bio_molecules(formula);
+
+CREATE INDEX idx_bio_user_chal   ON bio_user_challenges(user_id);
+
+CREATE INDEX idx_bio_user_mol    ON bio_user_molecules(user_id);
+
+CREATE INDEX idx_blocks_lesson ON lesson_blocks(lesson_id);
+
+CREATE INDEX idx_bookmarks_user ON bookmarks(user_id);
+
+CREATE INDEX idx_cc_class  ON class_courses(class_id);
+
+CREATE INDEX idx_cc_course ON class_courses(course_id);
+
+CREATE INDEX idx_challenges_user_week ON challenges(user_id, week);
+
+CREATE INDEX idx_class_members_class ON class_members(class_id);
+
+CREATE INDEX idx_class_members_user  ON class_members(user_id);
+
+CREATE INDEX idx_courses_creator ON courses(created_by);
+
+CREATE INDEX idx_courses_subject ON courses(subject_slug);
+
+CREATE INDEX idx_cr_chat ON classroom_chat(session_id);
+
+CREATE INDEX idx_cr_reactions ON classroom_chat_reactions(chat_id);
+
+CREATE INDEX idx_cr_sessions_class ON classroom_sessions(class_id, status);
+
+CREATE INDEX idx_cr_strokes ON classroom_strokes(session_id, page_num, seq);
+
+CREATE INDEX idx_ctpl_creator ON course_templates(created_by);
+
+CREATE INDEX idx_ctpl_public  ON course_templates(is_public);
+
+CREATE INDEX idx_daily_goals_user ON daily_goals(user_id, date);
+
+CREATE INDEX idx_error_log_date ON error_log(created_at DESC);
+
+CREATE INDEX idx_file_access_file ON file_access(file_id);
+
+CREATE INDEX idx_files_subject  ON files(subject_slug);
+
+CREATE INDEX idx_files_uploader ON files(uploaded_by);
+
+CREATE INDEX idx_folder_access_folder ON folder_access(folder_id);
+
+CREATE INDEX idx_geo_subs_student ON geometry_submissions(student_id);
+
+CREATE INDEX idx_geo_subs_task ON geometry_submissions(task_id);
+
+CREATE INDEX idx_geo_tasks_teacher ON geometry_tasks(teacher_id);
+
+CREATE INDEX idx_lcomments_lesson ON lesson_comments(lesson_id);
+
+CREATE INDEX idx_lcomments_parent ON lesson_comments(parent_id);
+
+CREATE INDEX idx_lcomments_user   ON lesson_comments(user_id);
+
+CREATE INDEX idx_lessons_course ON lessons(course_id);
+
+CREATE INDEX idx_live_answers_question ON live_answers(live_session_id, question_id);
+
+CREATE INDEX idx_live_answers_session ON live_answers(live_session_id);
+
+CREATE INDEX idx_live_sessions_class  ON live_sessions(class_id, status);
+
+CREATE INDEX idx_lprogress_lesson ON lesson_progress(lesson_id);
+
+CREATE INDEX idx_lprogress_user   ON lesson_progress(user_id);
+
+CREATE INDEX idx_ltpl_creator ON lesson_templates(created_by);
+
+CREATE INDEX idx_ltpl_public  ON lesson_templates(is_public);
+
+CREATE INDEX idx_notes_lesson ON lesson_notes(lesson_id);
+
+CREATE INDEX idx_notes_user   ON lesson_notes(user_id);
+
+CREATE INDEX idx_notifications_user ON notifications(user_id, is_read);
+
+CREATE INDEX idx_parent_links_student ON parent_links(student_id);
+
+CREATE INDEX idx_parent_links_token   ON parent_links(token);
+
+CREATE INDEX idx_parent_notif_link ON parent_notifications(parent_link_id, is_read);
+
+CREATE INDEX idx_parent_notif_link_date ON parent_notifications(parent_link_id, created_at DESC);
+
+CREATE INDEX idx_purchases_user ON user_purchases(user_id);
+
+CREATE INDEX idx_questions_source ON questions(source_type);
+
+CREATE INDEX idx_questions_subject ON questions(subject_id);
+
+CREATE INDEX idx_questions_topic   ON questions(topic_id);
+
+CREATE INDEX idx_rb_collection_user  ON rb_user_collection(user_id);
+
+CREATE INDEX idx_rb_popdata_species  ON rb_population_data(species_id);
+
+CREATE INDEX idx_rb_sightings_user   ON rb_sightings(user_id);
+
+CREATE INDEX idx_rb_species_category ON rb_species(category);
+
+CREATE INDEX idx_rb_species_group    ON rb_species(group_id);
+
+CREATE INDEX idx_sections_course ON course_sections(course_id);
+
+CREATE INDEX idx_sessions_user     ON test_sessions(user_id);
+
+CREATE INDEX idx_sessions_user_status ON test_sessions(user_id, status);
+
+CREATE INDEX idx_sessions_user_status_date ON test_sessions(user_id, status, started_at DESC);
+
+CREATE INDEX idx_sq_session           ON session_questions(session_id);
+
+CREATE INDEX idx_submissions_assignment ON submissions(assignment_id);
+
+CREATE INDEX idx_submissions_class      ON submissions(class_id);
+
+CREATE INDEX idx_submissions_student    ON submissions(student_id);
+
+CREATE INDEX idx_test_sessions_status     ON test_sessions(status);
+
+CREATE INDEX idx_test_sessions_user_status ON test_sessions(user_id, status);
+
+CREATE UNIQUE INDEX idx_topics_uniq ON topics(subject_id, name);
+
+CREATE INDEX idx_tpl_creator ON assignment_templates(created_by);
+
+CREATE INDEX idx_user_achievements_user ON user_achievements(user_id);
+
+CREATE INDEX idx_user_permissions_user ON user_permissions(user_id);
+
+CREATE INDEX idx_xp_log_date ON xp_log(created_at);
+
+CREATE INDEX idx_xp_log_user ON xp_log(user_id);
+
+CREATE INDEX idx_xp_log_user_created       ON xp_log(user_id, created_at);
diff --git a/backend/src/db/migrations/001_init.sql b/backend/src/db/migrations/001_init.sql
deleted file mode 100644
index 482d09e..0000000
--- a/backend/src/db/migrations/001_init.sql
+++ /dev/null
@@ -1,102 +0,0 @@
--- =============================================
---  LearnSpace — Initial schema
--- =============================================
-
--- Расширения
-CREATE EXTENSION IF NOT EXISTS "pgcrypto";
-
--- ── Пользователи ──────────────────────────────
-CREATE TABLE IF NOT EXISTS users (
-  id            SERIAL PRIMARY KEY,
-  email         VARCHAR(255) UNIQUE NOT NULL,
-  password_hash VARCHAR(255) NOT NULL,
-  name          VARCHAR(255) NOT NULL,
-  role          VARCHAR(20)  NOT NULL DEFAULT 'student'
-                CHECK (role IN ('student', 'teacher', 'admin')),
-  created_at    TIMESTAMPTZ  NOT NULL DEFAULT NOW(),
-  last_login    TIMESTAMPTZ
-);
-
--- ── Предметы ──────────────────────────────────
-CREATE TABLE IF NOT EXISTS subjects (
-  id   SERIAL PRIMARY KEY,
-  slug VARCHAR(50) UNIQUE NOT NULL,
-  name VARCHAR(100) NOT NULL,
-  icon VARCHAR(10)
-);
-
-INSERT INTO subjects (slug, name, icon) VALUES
-  ('bio',  'Биология',   'dna'),
-  ('chem', 'Химия',      'atom'),
-  ('math', 'Математика', 'compass'),
-  ('phys', 'Физика',     'zap')
-ON CONFLICT DO NOTHING;
-
--- ── Темы ──────────────────────────────────────
-CREATE TABLE IF NOT EXISTS topics (
-  id          SERIAL PRIMARY KEY,
-  subject_id  INT NOT NULL REFERENCES subjects(id) ON DELETE CASCADE,
-  name        VARCHAR(255) NOT NULL,
-  order_index INT NOT NULL DEFAULT 0
-);
-
--- ── Банк вопросов ─────────────────────────────
-CREATE TABLE IF NOT EXISTS questions (
-  id          SERIAL PRIMARY KEY,
-  subject_id  INT  NOT NULL REFERENCES subjects(id) ON DELETE CASCADE,
-  topic_id    INT  REFERENCES topics(id) ON DELETE SET NULL,
-  text        TEXT NOT NULL,
-  difficulty  SMALLINT NOT NULL DEFAULT 1 CHECK (difficulty BETWEEN 1 AND 3),
-  year        SMALLINT,
-  explanation TEXT,
-  created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
-);
-
--- ── Варианты ответов ──────────────────────────
-CREATE TABLE IF NOT EXISTS options (
-  id          SERIAL PRIMARY KEY,
-  question_id INT  NOT NULL REFERENCES questions(id) ON DELETE CASCADE,
-  text        TEXT NOT NULL,
-  is_correct  BOOLEAN NOT NULL DEFAULT FALSE,
-  order_index SMALLINT NOT NULL DEFAULT 0
-);
-
--- ── Сессии тестирования ───────────────────────
-CREATE TABLE IF NOT EXISTS test_sessions (
-  id           SERIAL PRIMARY KEY,
-  user_id      INT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
-  subject_id   INT REFERENCES subjects(id) ON DELETE SET NULL,
-  mode         VARCHAR(20) NOT NULL DEFAULT 'exam'
-               CHECK (mode IN ('exam', 'practice', 'topic', 'random')),
-  total        INT NOT NULL,
-  score        INT,
-  status       VARCHAR(20) NOT NULL DEFAULT 'in_progress'
-               CHECK (status IN ('in_progress', 'completed', 'abandoned')),
-  started_at   TIMESTAMPTZ NOT NULL DEFAULT NOW(),
-  finished_at  TIMESTAMPTZ
-);
-
--- ── Вопросы сессии ────────────────────────────
-CREATE TABLE IF NOT EXISTS session_questions (
-  id          SERIAL PRIMARY KEY,
-  session_id  INT NOT NULL REFERENCES test_sessions(id) ON DELETE CASCADE,
-  question_id INT NOT NULL REFERENCES questions(id),
-  order_index INT NOT NULL
-);
-
--- ── Ответы пользователя ───────────────────────
-CREATE TABLE IF NOT EXISTS user_answers (
-  id               SERIAL PRIMARY KEY,
-  session_id       INT NOT NULL REFERENCES test_sessions(id) ON DELETE CASCADE,
-  question_id      INT NOT NULL REFERENCES questions(id),
-  chosen_option_id INT REFERENCES options(id),
-  is_correct       BOOLEAN,
-  time_spent_sec   SMALLINT,
-  answered_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
-);
-
--- ── Индексы ───────────────────────────────────
-CREATE INDEX IF NOT EXISTS idx_questions_subject ON questions(subject_id);
-CREATE INDEX IF NOT EXISTS idx_questions_topic   ON questions(topic_id);
-CREATE INDEX IF NOT EXISTS idx_sessions_user     ON test_sessions(user_id);
-CREATE INDEX IF NOT EXISTS idx_answers_session   ON user_answers(session_id);
diff --git a/backend/src/db/migrations/002_constraints.sql b/backend/src/db/migrations/002_constraints.sql
deleted file mode 100644
index cb69e10..0000000
--- a/backend/src/db/migrations/002_constraints.sql
+++ /dev/null
@@ -1,3 +0,0 @@
--- Уникальный индекс для upsert ответов
-CREATE UNIQUE INDEX IF NOT EXISTS idx_answers_session_question
-  ON user_answers (session_id, question_id);
diff --git a/backend/src/db/migrations/README.md b/backend/src/db/migrations/README.md
new file mode 100644
index 0000000..70c1159
--- /dev/null
+++ b/backend/src/db/migrations/README.md
@@ -0,0 +1,63 @@
+# Versioned migrations
+
+Each schema change is a separate `.sql` file, applied in alphabetical order.
+Applied files are tracked in the `_migrations` table.
+
+## Applying migrations
+
+```sh
+npm run migrate           # apply pending migrations (safe to re-run)
+npm run migrate:bootstrap # mark 000_baseline.sql as applied on existing DB (run ONCE per env)
+npm run migrate:legacy    # run legacy migrate.js (kept for reference, do not use)
+```
+
+## Naming convention
+
+```
+NNN_short_description.sql
+```
+
+Examples: `001_add_user_avatar.sql`, `002_drop_unused_columns.sql`
+
+To find the next number:
+```sh
+ls backend/src/db/migrations/*.sql | sort -r | head -1
+```
+
+## Rules
+
+1. **Never edit** a migration file after it has been committed and deployed.
+2. To revert: write a new migration that undoes the change.
+3. Each file must be valid SQLite SQL (not PostgreSQL — no SERIAL, no EXTENSION).
+4. Use `IF NOT EXISTS` / `IF EXISTS` where possible for safety.
+5. Test on a copy of the prod DB before deploying.
+
+## Deploy order (first time on a new environment)
+
+```sh
+npm run migrate:legacy        # initialize full schema (existing init script)
+npm run seed:permissions      # seed default permissions and achievements
+npm run migrate:bootstrap     # mark 000_baseline.sql as applied
+npm run migrate               # apply any newer migrations (should say "nothing to apply")
+npm start
+```
+
+## Adding a new migration
+
+```sh
+# 1. Create the file
+echo "ALTER TABLE users ADD COLUMN avatar_url TEXT;" > backend/src/db/migrations/001_add_avatar_url.sql
+
+# 2. Apply and verify
+npm run migrate
+
+# 3. Commit
+git add backend/src/db/migrations/001_add_avatar_url.sql
+git commit -m "db: add avatar_url column to users"
+```
+
+## Files
+
+| File | Description |
+|------|-------------|
+| `000_baseline.sql` | Snapshot of full schema as of 2026-05-06. Never runs on existing DBs. |