Phase 3.1: Complete client_app Riverpod migration (all blocs)

- Migrate SessionClosureBloc → SessionClosureNotifier (@riverpod)
- Migrate PairingBloc → PairingNotifier (@riverpod, WebSocket + timer)
- Migrate ChatBloc → ChatNotifier (@riverpod, WebSocket + message state)
- Remove all flutter_bloc usage from client_app screens and main.dart
- MultiBlocProvider fully removed from client_app
- All screens now use ConsumerWidget/ConsumerStatefulWidget + ref

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

client_app/lib/main.dart

@@ -1,13 +1,9 @@
 import 'package:firebase_core/firebase_core.dart';
 import 'package:firebase_messaging/firebase_messaging.dart';
 import 'package:flutter/material.dart';
-import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'core/api/api_client_provider.dart';
 import 'core/auth/auth_notifier.dart';
-import 'core/chat/chat_bloc.dart';
-import 'core/chat/session_closure_bloc.dart';
-import 'core/pairing/pairing_bloc.dart';
 import 'core/notifications/notification_service.dart';
 import 'firebase_options.dart';
 import 'router.dart';
@@ -49,7 +45,6 @@ class _AppState extends ConsumerState<App> {
 
   @override
   Widget build(BuildContext context) {
-    // Listen for auth changes to register FCM token
     ref.listen(authProvider, (prev, next) {
       final data = next.valueOrNull;
       if (data is AuthAuthenticatedData || data is AuthAnonymousData) {
@@ -58,23 +53,12 @@ class _AppState extends ConsumerState<App> {
     });
 
     final router = ref.watch(routerProvider);
-    final apiClient = ref.watch(apiClientProvider);
 
-    // Initialize notifications once router is available
     NotificationService.initialize(router);
 
-    // Keep BlocProviders for non-migrated blocs (will be removed as they're migrated)
-    return MultiBlocProvider(
-      providers: [
-        BlocProvider(create: (_) => PairingBloc(apiClient: apiClient)),
-        BlocProvider(create: (_) => ChatBloc(apiClient: apiClient)),
-        BlocProvider(create: (_) => SessionClosureBloc(apiClient: apiClient)),
-        RepositoryProvider.value(value: apiClient),
-      ],
-      child: MaterialApp.router(
-        title: 'Halo Bestie',
-        routerConfig: router,
-      ),
+    return MaterialApp.router(
+      title: 'Halo Bestie',
+      routerConfig: router,
     );
   }
 }