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/chat/widgets/pricing_bottom_sheet.dart

@@ -1,9 +1,8 @@
 import 'package:flutter/material.dart';
-import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import '../../../core/chat/chat_opening_provider.dart';
-import '../../../core/chat/session_closure_bloc.dart';
-import '../../../core/pairing/pairing_bloc.dart';
+import '../../../core/chat/session_closure_notifier.dart';
+import '../../../core/pairing/pairing_notifier.dart';
 
 class PricingBottomSheet extends ConsumerWidget {
   /// If set, the bottom sheet is in "extension" mode — selecting a tier extends the session.
@@ -16,12 +15,7 @@ class PricingBottomSheet extends ConsumerWidget {
     return showModalBottomSheet(
       context: context,
       isScrollControlled: true,
-      builder: (_) => MultiBlocProvider(
-        providers: [
-          BlocProvider.value(value: context.read<PairingBloc>()),
-        ],
-        child: const PricingBottomSheet(),
-      ),
+      builder: (_) => const PricingBottomSheet(),
     );
   }
 
@@ -30,12 +24,7 @@ class PricingBottomSheet extends ConsumerWidget {
     return showModalBottomSheet(
       context: context,
       isScrollControlled: true,
-      builder: (_) => MultiBlocProvider(
-        providers: [
-          BlocProvider.value(value: context.read<SessionClosureBloc>()),
-        ],
-        child: PricingBottomSheet(extensionSessionId: sessionId),
-      ),
+      builder: (_) => PricingBottomSheet(extensionSessionId: sessionId),
     );
   }
 
@@ -90,7 +79,7 @@ class PricingBottomSheet extends ConsumerWidget {
                       trailing: const Icon(Icons.arrow_forward_ios, size: 16),
                       onTap: () {
                         Navigator.of(context).pop();
-                        _startPairing(context, isFreeTrial: true);
+                        _startPairing(ref, isFreeTrial: true);
                       },
                     ),
                   ),
@@ -107,14 +96,14 @@ class PricingBottomSheet extends ConsumerWidget {
                       Navigator.of(context).pop();
                       if (isExtension) {
                         _requestExtension(
-                          context,
+                          ref,
                           sessionId: extensionSessionId!,
                           durationMinutes: tier.durationMinutes,
                           price: tier.price,
                         );
                       } else {
                         _startPairing(
-                          context,
+                          ref,
                           durationMinutes: tier.durationMinutes,
                           price: tier.price,
                         );
@@ -130,19 +119,19 @@ class PricingBottomSheet extends ConsumerWidget {
     );
   }
 
-  void _startPairing(BuildContext context, {bool isFreeTrial = false, int? durationMinutes, int? price}) {
-    context.read<PairingBloc>().add(RequestPairingWithTier(
+  void _startPairing(WidgetRef ref, {bool isFreeTrial = false, int? durationMinutes, int? price}) {
+    ref.read(pairingProvider.notifier).requestPairingWithTier(
       durationMinutes: durationMinutes,
       price: price,
       isFreeTrial: isFreeTrial,
-    ));
+    );
   }
 
-  void _requestExtension(BuildContext context, {required String sessionId, required int durationMinutes, required int price}) {
-    context.read<SessionClosureBloc>().add(RequestExtension(
-      sessionId: sessionId,
+  void _requestExtension(WidgetRef ref, {required String sessionId, required int durationMinutes, required int price}) {
+    ref.read(sessionClosureProvider.notifier).requestExtension(
+      sessionId,
       durationMinutes: durationMinutes,
       price: price,
-    ));
+    );
   }
 }