feat: add groupId support and redesign schedule GroupView hierarchy

- Add groupId field to ScheduleClass for admin-defined group identity
- Add versioned DB migration system (replaces initTables) to prevent data loss
- Redesign GroupView: Trainer → Class Type → Group → Datetimes hierarchy
- Group datetimes by day, merge days with identical time sets
- Auto-assign groupIds to legacy schedule entries in admin
- Add mc_registrations CRUD to db.ts

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/lib/db.ts

@@ -13,50 +13,104 @@ function getDb(): Database.Database {
     _db = new Database(DB_PATH);
     _db.pragma("journal_mode = WAL");
     _db.pragma("foreign_keys = ON");
-    initTables(_db);
+    runMigrations(_db);
   }
   return _db;
 }
 
-function initTables(db: Database.Database) {
+// --- Migrations ---
+// Each migration has a unique version number and runs exactly once.
+// Add new migrations to the end of the array. Never modify existing ones.
+
+interface Migration {
+  version: number;
+  name: string;
+  up: (db: Database.Database) => void;
+}
+
+const migrations: Migration[] = [
+  {
+    version: 1,
+    name: "create_sections_and_team_members",
+    up: (db) => {
+      db.exec(`
+        CREATE TABLE IF NOT EXISTS sections (
+          key TEXT PRIMARY KEY,
+          data TEXT NOT NULL,
+          updated_at TEXT DEFAULT (datetime('now'))
+        );
+        CREATE TABLE IF NOT EXISTS team_members (
+          id INTEGER PRIMARY KEY AUTOINCREMENT,
+          name TEXT NOT NULL,
+          role TEXT NOT NULL,
+          image TEXT NOT NULL,
+          instagram TEXT,
+          description TEXT,
+          sort_order INTEGER NOT NULL DEFAULT 0,
+          created_at TEXT DEFAULT (datetime('now')),
+          updated_at TEXT DEFAULT (datetime('now'))
+        );
+      `);
+    },
+  },
+  {
+    version: 2,
+    name: "add_team_bio_columns",
+    up: (db) => {
+      const cols = db.prepare("PRAGMA table_info(team_members)").all() as { name: string }[];
+      const colNames = new Set(cols.map((c) => c.name));
+      if (!colNames.has("experience")) db.exec("ALTER TABLE team_members ADD COLUMN experience TEXT");
+      if (!colNames.has("victories")) db.exec("ALTER TABLE team_members ADD COLUMN victories TEXT");
+      if (!colNames.has("education")) db.exec("ALTER TABLE team_members ADD COLUMN education TEXT");
+    },
+  },
+  {
+    version: 3,
+    name: "create_mc_registrations",
+    up: (db) => {
+      db.exec(`
+        CREATE TABLE IF NOT EXISTS mc_registrations (
+          id INTEGER PRIMARY KEY AUTOINCREMENT,
+          master_class_title TEXT NOT NULL,
+          name TEXT NOT NULL,
+          instagram TEXT NOT NULL,
+          telegram TEXT,
+          created_at TEXT DEFAULT (datetime('now'))
+        );
+      `);
+    },
+  },
+];
+
+function runMigrations(db: Database.Database) {
+  // Create migrations tracking table
   db.exec(`
-    CREATE TABLE IF NOT EXISTS sections (
-      key TEXT PRIMARY KEY,
-      data TEXT NOT NULL,
-      updated_at TEXT DEFAULT (datetime('now'))
-    );
-
-    CREATE TABLE IF NOT EXISTS mc_registrations (
-      id INTEGER PRIMARY KEY AUTOINCREMENT,
-      master_class_title TEXT NOT NULL,
+    CREATE TABLE IF NOT EXISTS _migrations (
+      version INTEGER PRIMARY KEY,
       name TEXT NOT NULL,
-      instagram TEXT NOT NULL,
-      telegram TEXT,
-      created_at TEXT DEFAULT (datetime('now'))
-    );
-
-    CREATE TABLE IF NOT EXISTS team_members (
-      id INTEGER PRIMARY KEY AUTOINCREMENT,
-      name TEXT NOT NULL,
-      role TEXT NOT NULL,
-      image TEXT NOT NULL,
-      instagram TEXT,
-      description TEXT,
-      experience TEXT,
-      victories TEXT,
-      education TEXT,
-      sort_order INTEGER NOT NULL DEFAULT 0,
-      created_at TEXT DEFAULT (datetime('now')),
-      updated_at TEXT DEFAULT (datetime('now'))
+      applied_at TEXT DEFAULT (datetime('now'))
     );
   `);
 
-  // Migrate: add bio columns if missing
-  const cols = db.prepare("PRAGMA table_info(team_members)").all() as { name: string }[];
-  const colNames = new Set(cols.map((c) => c.name));
-  if (!colNames.has("experience")) db.exec("ALTER TABLE team_members ADD COLUMN experience TEXT");
-  if (!colNames.has("victories")) db.exec("ALTER TABLE team_members ADD COLUMN victories TEXT");
-  if (!colNames.has("education")) db.exec("ALTER TABLE team_members ADD COLUMN education TEXT");
+  const applied = new Set(
+    (db.prepare("SELECT version FROM _migrations").all() as { version: number }[])
+      .map((r) => r.version)
+  );
+
+  const pending = migrations.filter((m) => !applied.has(m.version));
+  if (pending.length === 0) return;
+
+  const insertMigration = db.prepare(
+    "INSERT INTO _migrations (version, name) VALUES (?, ?)"
+  );
+
+  const tx = db.transaction(() => {
+    for (const m of pending) {
+      m.up(db);
+      insertMigration.run(m.version, m.name);
+    }
+  });
+  tx();
 }
 
 // --- Sections ---