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/features/chat/models/request_history_entry.dart

@@ -0,0 +1,42 @@
+import '../../../core/constants.dart';
+
+class RequestHistoryEntry {
+  final String notificationId;
+  final String sessionId;
+  final DateTime notifiedAt;
+  final DateTime? respondedAt;
+  final RequestResponse? response;
+  final String sessionStatus;
+  final String customerCallName;
+  final TopicSensitivity topicSensitivity;
+
+  const RequestHistoryEntry({
+    required this.notificationId,
+    required this.sessionId,
+    required this.notifiedAt,
+    required this.respondedAt,
+    required this.response,
+    required this.sessionStatus,
+    required this.customerCallName,
+    required this.topicSensitivity,
+  });
+
+  bool get isPending =>
+      response == null && sessionStatus == SessionStatus.pendingAcceptance;
+
+  factory RequestHistoryEntry.fromJson(Map<String, dynamic> json) {
+    return RequestHistoryEntry(
+      notificationId: json['notification_id'] as String,
+      sessionId: json['session_id'] as String,
+      notifiedAt: DateTime.parse(json['notified_at'] as String).toLocal(),
+      respondedAt: json['responded_at'] != null
+          ? DateTime.parse(json['responded_at'] as String).toLocal()
+          : null,
+      response: RequestResponse.fromString(json['response'] as String?),
+      sessionStatus: json['session_status'] as String? ?? '',
+      customerCallName: json['customer_call_name'] as String? ?? 'Anonim',
+      topicSensitivity:
+          TopicSensitivity.fromString(json['topic_sensitivity'] as String?),
+    );
+  }
+}