Add pending chat requests CTA on mitra home screen

- Backend: new GET /api/mitra/chat-requests/pending endpoint
- Backend: getPendingRequestsForMitra() queries unresponded notifications
  for sessions still in pending_acceptance status
- Mitra app: loadPendingRequests() fetches on screen load + status toggle
- Mitra app: activeRequestCount getter exposes queue size
- Mitra app: _PendingRequestsBanner widget shows count with tap-to-view

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

mitra_app/lib/core/chat/chat_request_notifier.dart

@@ -72,9 +72,54 @@ class ChatRequest extends _$ChatRequest {
 
   ApiClient get _apiClient => ref.read(apiClientProvider);
 
+  /// Number of active requests (currently displayed + queued).
+  int get activeRequestCount {
+    final current = state is ChatRequestIncomingData ? 1 : 0;
+    return current + _pendingQueue.length;
+  }
+
   @override
   ChatRequestData build() => const ChatRequestIdleData();
 
+  /// Fetch pending requests from backend and populate the queue.
+  Future<void> loadPendingRequests() async {
+    try {
+      final response = await _apiClient.get('/api/mitra/chat-requests/pending');
+      final requests = response['data'] as List<dynamic>;
+      if (requests.isEmpty) return;
+
+      for (final r in requests) {
+        final sessionId = r['session_id'] as String;
+        // Skip if already showing or queued
+        if (state is ChatRequestIncomingData &&
+            (state as ChatRequestIncomingData).sessionId == sessionId) continue;
+        if (_pendingQueue.any((q) => q['session_id'] == sessionId)) continue;
+
+        final data = {
+          'session_id': sessionId,
+          'duration_minutes': r['duration_minutes'],
+          'is_free_trial': r['is_free_trial'],
+          'created_at': r['created_at'],
+        };
+
+        if (state is ChatRequestIncomingData ||
+            state is ChatRequestStaleData ||
+            state is ChatRequestAcceptingData) {
+          _pendingQueue.add(data);
+        } else {
+          state = ChatRequestIncomingData(
+            sessionId,
+            durationMinutes: r['duration_minutes'] as int?,
+            isFreeTrial: r['is_free_trial'] as bool?,
+            createdAt: r['created_at'] != null
+                ? DateTime.tryParse(r['created_at'] as String)
+                : null,
+          );
+        }
+      }
+    } catch (_) {}
+  }
+
   Future<void> startListening() async {
     // Don't reset state if showing a request, stale message, or actively accepting
     if (state is ChatRequestIncomingData ||