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/app.internal.js

@@ -6,6 +6,7 @@ import { rolesRoutes } from './routes/internal/roles.routes.js'
 import { internalAuthRoutes } from './routes/internal/auth.routes.js'
 import { internalConfigRoutes } from './routes/internal/config.routes.js'
 import { sessionManagementRoutes } from './routes/internal/session.routes.js'
+import { mitraActivityRoutes } from './routes/internal/mitra-activity.routes.js'
 import { errorHandler } from './plugins/error-handler.js'
 
 export const buildInternalApp = async () => {
@@ -20,6 +21,7 @@ export const buildInternalApp = async () => {
   app.register(rolesRoutes, { prefix: '/internal/roles' })
   app.register(internalConfigRoutes, { prefix: '/internal/config' })
   app.register(sessionManagementRoutes, { prefix: '/internal/sessions' })
+  app.register(mitraActivityRoutes, { prefix: '/internal/mitra-activity' })
 
   return app
 }