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>

control_center/src/components/Layout.jsx

@@ -13,6 +13,7 @@ export default function Layout() {
           <li><NavLink to="/mitras">Mitra</NavLink></li>
           <li><NavLink to="/sessions">Sesi</NavLink></li>
           <li><NavLink to="/users">Users</NavLink></li>
+          <li><NavLink to="/mitra-activity">Aktivitas Mitra</NavLink></li>
           <li><NavLink to="/settings">Settings</NavLink></li>
         </ul>
         <div style={{ marginTop: 'auto', paddingTop: 16 }}>