Phase 3 scaffold: chat engine (WebSocket, FCM, pricing, timer, extension, history)

- Backend: WebSocket plugin, chat/pricing/timer/extension/closure/notification services
- Client app: ChatBloc, pricing dialog, chat screen with message status, extension/goodbye flow, history
- Mitra app: MitraChatBloc, ExtensionBloc, chat screen, extension accept/reject, history
- Control center: free trial, extension timeout, early end config toggles
- DB migration: chat_messages, session_closures, session_extensions, customer_transactions tables

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

client_app/lib/router.dart

@@ -11,7 +11,9 @@ import 'features/home/home_screen.dart';
 import 'features/chat/screens/searching_screen.dart';
 import 'features/chat/screens/bestie_found_screen.dart';
 import 'features/chat/screens/no_bestie_screen.dart';
-import 'features/chat/screens/session_active_screen.dart';
+import 'features/chat/screens/chat_screen.dart';
+import 'features/chat/screens/chat_history_screen.dart';
+import 'features/chat/screens/chat_transcript_screen.dart';
 
 /// Converts a BLoC stream into a ChangeNotifier for GoRouter's refreshListenable.
 class _BlocRefreshNotifier extends ChangeNotifier {
@@ -64,11 +66,16 @@ GoRouter buildRouter(AuthBloc authBloc) {
       }),
       GoRoute(path: '/chat/no-bestie', builder: (_, __) => const NoBestieScreen()),
       GoRoute(path: '/chat/session/:sessionId', builder: (context, state) {
-        return SessionActiveScreen(
+        final extra = state.extra as Map<String, dynamic>?;
+        return ChatScreen(
           sessionId: state.pathParameters['sessionId']!,
-          mitraName: state.extra as String? ?? 'Bestie',
+          mitraName: extra?['mitraName'] as String? ?? 'Bestie',
         );
       }),
+      GoRoute(path: '/chat/history', builder: (_, __) => const ChatHistoryScreen()),
+      GoRoute(path: '/chat/history/:sessionId', builder: (context, state) {
+        return ChatTranscriptScreen(sessionId: state.pathParameters['sessionId']!);
+      }),
     ],
   );
 }