feat(dashboard): блок активности — все виды учёбы, тренд, разбивка по типам, empty-state

- Бэкенд /api/dashboard/activity: per-day агрегация активности по типам (тест/экзамен/карты/уроки/
  онлайн/домашка) из 6 таблиц за ~182 дня (раньше карта считала только тесты).
- Карта раскрашивается по доминирующему типу активности + легенда типов; интенсивность/размер по числу.
- Недельный тренд в футере («эта неделя N · +K к прошлой»).
- Тултип и попап по клику показывают разбивку дня по типам.
- Empty-state для новичков (вместо пустой сетки — призыв + CTA). Календарь «Месяц» тоже от всех активностей.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/routes/dashboard.js

@@ -0,0 +1,47 @@
+'use strict';
+/* Dashboard aggregates. /api/dashboard/activity — per-day study activity of the
+ * current user across ALL engagement types (not just tests), for the activity
+ * heatmap. Each source contributes a per-day count by type. */
+const express = require('express');
+const router  = express.Router();
+const db = require('../db/db');
+const { authMiddleware } = require('../middleware/auth');
+
+router.use(authMiddleware);
+
+const WINDOW_DAYS = 182; // ~6 months (max heatmap scale)
+
+/* GET /api/dashboard/activity → { days: { 'YYYY-MM-DD': { test, exam, cards, lesson, live, homework } } } */
+router.get('/activity', (req, res) => {
+  const uid = req.user.id;
+  const days = {};
+  const add = (d, type, n) => {
+    if (!d || !n) return;
+    (days[d] || (days[d] = {}))[type] = (days[d][type] || 0) + n;
+  };
+  // TEXT datetime sources use a SQL cutoff; exam_attempts stores epoch-ms.
+  const txtCut = `datetime('now','-${WINDOW_DAYS} days')`;
+  const epochCut = Date.now() - WINDOW_DAYS * 86400000;
+
+  const sources = [
+    ['test',     `SELECT DATE(started_at) d, COUNT(*) n FROM test_sessions
+                    WHERE user_id=? AND status='completed' AND started_at >= ${txtCut} GROUP BY d`, [uid]],
+    ['exam',     `SELECT DATE(created_at/1000,'unixepoch') d, COUNT(*) n FROM exam_attempts
+                    WHERE user_id=? AND created_at >= ? GROUP BY d`, [uid, epochCut]],
+    ['cards',    `SELECT DATE(last_reviewed) d, COUNT(*) n FROM flashcard_reviews
+                    WHERE user_id=? AND last_reviewed IS NOT NULL AND last_reviewed >= ${txtCut} GROUP BY d`, [uid]],
+    ['lesson',   `SELECT DATE(updated_at) d, COUNT(*) n FROM lesson_progress
+                    WHERE user_id=? AND completed=1 AND updated_at >= ${txtCut} GROUP BY d`, [uid]],
+    ['live',     `SELECT DATE(joined_at) d, COUNT(*) n FROM classroom_attendance
+                    WHERE user_id=? AND joined_at >= ${txtCut} GROUP BY d`, [uid]],
+    ['homework', `SELECT DATE(completed_at) d, COUNT(*) n FROM assignment_completion
+                    WHERE user_id=? AND completed_at >= ${txtCut} GROUP BY d`, [uid]],
+  ];
+  for (const [type, sql, args] of sources) {
+    try { db.prepare(sql).all(...args).forEach(r => add(r.d, type, r.n)); }
+    catch (e) { /* tolerate a missing/legacy table — skip that source */ }
+  }
+  res.json({ days });
+});
+
+module.exports = router;

backend/src/server.js

@@ -194,6 +194,7 @@ app.use('/api/access',       accessRoutes);
 app.use('/api/teacher-students', teacherStudentsRoutes);
 app.use('/api/lab',          labRoutes);
 app.use('/api/materials',    require('./routes/materials'));
+app.use('/api/dashboard',    require('./routes/dashboard'));
 
 /* ── Public features endpoint (merges global + per-class for authenticated students) ── */
 const _featDb = require('./db/db');