Phase 3.5: Mitra Chat Request History (backend route + mitra app screens)

Replaces the home-screen pending-requests banner with a "Riwayat
Permintaan" CTA that opens a list of the mitra's last 20 chat requests
(any status). Pending rows pin to the top; non-pending rows open a
read-only detail screen with a "Lihat percakapan" CTA on accepted rows.

Backend:
- New service `getRecentRequestsForMitra(mitraId, { limit })` capped at
  20, pending pinned via `(response IS NULL AND status='pending_acceptance')
  DESC`. Customer call_name returned verbatim, with `'Anonim'` only as
  null-safety fallback (no anonymity-flag masking — see project memory).
- New route `GET /api/mitra/chat-requests/recent`. Strictly per-mitra
  scoped via the existing `resolveMitra` preHandler.

Mitra app:
- New `RequestResponse` enum in core/constants.dart.
- New Riverpod notifier `requestHistoryProvider` (AsyncValue<List<...>>,
  keepAlive) — pull-to-refresh + screen-mount fetch only, no WS.
- Two new screens (history list + detail) and two new GoRoutes.
- Home screen: `_PendingRequestsBanner` removed → `_RequestHistoryButton`
  Card with red count badge. Live count comes from the existing
  chatRequestProvider so nothing changes about the WS-driven badge math.

Plan + acceptance criteria in requirement/phase3.5-plan.md. flutter
analyze clean (zero new issues). Backend smoke-tested against real DB.
Real-device E2E pending.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

mitra_app/lib/router.dart

@@ -10,6 +10,8 @@ import 'features/chat/screens/active_sessions_screen.dart';
 import 'features/chat/screens/mitra_chat_screen.dart';
 import 'features/chat/screens/chat_history_screen.dart';
 import 'features/chat/screens/chat_transcript_screen.dart';
+import 'features/chat/screens/request_history_screen.dart';
+import 'features/chat/screens/request_history_detail_screen.dart';
 
 class RouterNotifier extends ChangeNotifier {
   final Ref _ref;
@@ -71,6 +73,16 @@ GoRouter buildRouter(Ref ref) {
       GoRoute(path: '/chat/history/:sessionId', builder: (context, state) {
         return MitraChatTranscriptScreen(sessionId: state.pathParameters['sessionId']!);
       }),
+      GoRoute(
+        path: '/chat/requests/history',
+        builder: (_, __) => const RequestHistoryScreen(),
+      ),
+      GoRoute(
+        path: '/chat/requests/history/:notificationId',
+        builder: (context, state) => RequestHistoryDetailScreen(
+          notificationId: state.pathParameters['notificationId']!,
+        ),
+      ),
     ],
   );
 }