Phase 3.2 WS2: Mitra request activity log + control center page

- DB migration: add active_session_count column + mitra_notified index
- Constants: add MISSED to NotificationResponse
- Pairing service: record active_session_count on notification creation,
  use MISSED (not IGNORED) when another mitra accepts first
- New mitra-activity.service.js: getMitraActivityLog (paginated),
  getMitraActivitySummary (per-mitra aggregates with acceptance rate)
- New mitra-activity.routes.js: GET /internal/mitra-activity/log,
  GET /internal/mitra-activity/summary
- Control center: new MitraActivityPage with summary table + detail log,
  filters (mitra, date range), color-coded response types, pagination
- Register route in App.jsx, add "Aktivitas Mitra" nav link in Layout

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/src/db/migrate.js

@@ -288,6 +288,18 @@ const migrate = async () => {
     ON CONFLICT (key) DO NOTHING
   `
 
+  // --- Phase 3.2: Mitra Request Activity Log ---
+
+  await sql`
+    ALTER TABLE chat_request_notifications
+    ADD COLUMN IF NOT EXISTS active_session_count INT NOT NULL DEFAULT 0
+  `
+
+  await sql`
+    CREATE INDEX IF NOT EXISTS idx_chat_request_notifications_mitra_notified
+    ON chat_request_notifications (mitra_id, notified_at)
+  `
+
   console.log('Migration complete.')
   await sql.end()
 }