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/features/home/home_screen.dart

@@ -1,10 +1,9 @@
 import 'package:flutter/material.dart';
-import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 import '../../core/auth/auth_notifier.dart';
 import '../../core/api/api_client_provider.dart';
-import '../../core/pairing/pairing_bloc.dart';
+import '../../core/pairing/pairing_notifier.dart';
 import '../chat/widgets/pricing_bottom_sheet.dart';
 
 class HomeScreen extends ConsumerStatefulWidget {
@@ -71,19 +70,19 @@ class _HomeScreenState extends ConsumerState<HomeScreen> with WidgetsBindingObse
       _ => '',
     };
 
-    return BlocListener<PairingBloc, PairingState>(
-      listener: (context, state) {
-        if (state is PairingSearching) {
-          context.go('/chat/searching');
-        } else if (state is PairingNoBestie) {
-          context.go('/chat/no-bestie');
-        } else if (state is PairingError) {
-          ScaffoldMessenger.of(context).showSnackBar(
-            SnackBar(content: Text(state.message)),
-          );
-        }
-      },
-      child: Scaffold(
+    ref.listen(pairingProvider, (prev, next) {
+      if (next is PairingSearchingData) {
+        context.go('/chat/searching');
+      } else if (next is PairingNoBestieData) {
+        context.go('/chat/no-bestie');
+      } else if (next is PairingErrorData) {
+        ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(content: Text(next.message)),
+        );
+      }
+    });
+
+    return Scaffold(
         appBar: AppBar(
           title: const Text('Halo Bestie'),
           actions: [
@@ -130,7 +129,6 @@ class _HomeScreenState extends ConsumerState<HomeScreen> with WidgetsBindingObse
             ),
           ),
         ),
-      ),
     );
   }
 }