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/screens/bestie_found_screen.dart

@@ -1,9 +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/pairing/pairing_bloc.dart';
+import '../../../core/pairing/pairing_notifier.dart';
 
-class BestieFoundScreen extends StatelessWidget {
+class BestieFoundScreen extends ConsumerWidget {
   final String sessionId;
   final String mitraName;
 
@@ -14,36 +14,35 @@ class BestieFoundScreen extends StatelessWidget {
   });
 
   @override
-  Widget build(BuildContext context) {
-    return BlocListener<PairingBloc, PairingState>(
-      listener: (context, state) {
-        if (state is PairingActive) {
-          context.go('/chat/session/${state.sessionId}', extra: state.mitraName);
-        }
-      },
-      child: Scaffold(
-        body: Center(
-          child: Padding(
-            padding: const EdgeInsets.all(32),
-            child: Column(
-              mainAxisAlignment: MainAxisAlignment.center,
-              children: [
-                const Icon(Icons.check_circle, size: 80, color: Colors.green),
-                const SizedBox(height: 24),
-                const Text(
-                  'Bestie ditemukan!',
-                  style: TextStyle(fontSize: 24, fontWeight: FontWeight.bold),
-                ),
-                const SizedBox(height: 8),
-                Text(
-                  'Menghubungkan kamu ke $mitraName',
-                  textAlign: TextAlign.center,
-                  style: const TextStyle(fontSize: 16, color: Colors.grey),
-                ),
-                const SizedBox(height: 24),
-                const CircularProgressIndicator(),
-              ],
-            ),
+  Widget build(BuildContext context, WidgetRef ref) {
+    ref.listen(pairingProvider, (prev, next) {
+      if (next is PairingActiveData) {
+        context.go('/chat/session/${next.sessionId}', extra: next.mitraName);
+      }
+    });
+
+    return Scaffold(
+      body: Center(
+        child: Padding(
+          padding: const EdgeInsets.all(32),
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: [
+              const Icon(Icons.check_circle, size: 80, color: Colors.green),
+              const SizedBox(height: 24),
+              const Text(
+                'Bestie ditemukan!',
+                style: TextStyle(fontSize: 24, fontWeight: FontWeight.bold),
+              ),
+              const SizedBox(height: 8),
+              Text(
+                'Menghubungkan kamu ke $mitraName',
+                textAlign: TextAlign.center,
+                style: const TextStyle(fontSize: 16, color: Colors.grey),
+              ),
+              const SizedBox(height: 24),
+              const CircularProgressIndicator(),
+            ],
           ),
         ),
       ),