Phase 3.1: Complete mitra_app Riverpod migration (all blocs, fix auth bug)

- Migrate AuthBloc → MitraAuthNotifier (fixes stuck-loading bug: now returns
  MitraAuthInitialData when currentUser is null)
- Migrate StatusBloc → OnlineStatusNotifier (heartbeat timer + lifecycle)
- Migrate ExtensionBloc → MitraExtensionNotifier (accept/reject + goodbye)
- Migrate ChatRequestBloc → ChatRequestNotifier (WebSocket incoming requests)
- Migrate MitraChatBloc → MitraChatNotifier (WebSocket chat + messages)
- Update router to use Riverpod auth state for redirects
- Remove all flutter_bloc usage from mitra_app screens and main.dart
- MultiBlocProvider fully removed from mitra_app

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

mitra_app/lib/router.dart

@@ -1,7 +1,7 @@
-import 'dart:async';
 import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
-import 'core/auth/auth_bloc.dart';
+import 'core/auth/auth_notifier.dart';
 import 'features/splash/splash_screen.dart';
 import 'features/auth/screens/login_screen.dart';
 import 'features/auth/screens/otp_screen.dart';
@@ -11,34 +11,40 @@ import 'features/chat/screens/mitra_chat_screen.dart';
 import 'features/chat/screens/chat_history_screen.dart';
 import 'features/chat/screens/chat_transcript_screen.dart';
 
-class _BlocRefreshNotifier extends ChangeNotifier {
-  late final StreamSubscription _subscription;
+class RouterNotifier extends ChangeNotifier {
+  final Ref _ref;
 
-  _BlocRefreshNotifier(AuthBloc bloc) {
-    _subscription = bloc.stream.listen((_) => notifyListeners());
-  }
-
-  @override
-  void dispose() {
-    _subscription.cancel();
-    super.dispose();
+  RouterNotifier(this._ref) {
+    _ref.listen(mitraAuthProvider, (_, __) => notifyListeners());
   }
 }
 
-GoRouter buildRouter(AuthBloc authBloc) {
+final routerProvider = Provider<GoRouter>((ref) => buildRouter(ref));
+
+GoRouter buildRouter(Ref ref) {
+  final notifier = RouterNotifier(ref);
+
   return GoRouter(
     initialLocation: '/splash',
-    refreshListenable: _BlocRefreshNotifier(authBloc),
+    refreshListenable: notifier,
     redirect: (context, state) {
-      final authState = authBloc.state;
+      final authState = ref.read(mitraAuthProvider);
       final isSplash = state.matchedLocation == '/splash';
       final isAuthRoute = state.matchedLocation.startsWith('/login') ||
           state.matchedLocation.startsWith('/otp');
 
       // Show splash while loading
-      if (authState is AuthLoading) return isSplash ? null : '/splash';
+      if (authState is AsyncLoading) return isSplash ? null : '/splash';
 
-      if (authState is AuthAuthenticated) {
+      final data = authState.valueOrNull;
+      if (data == null) {
+        // Error state — show login
+        if (!isAuthRoute && !isSplash) return '/login';
+        if (isSplash) return '/login';
+        return null;
+      }
+
+      if (data is MitraAuthAuthenticatedData) {
         return (isSplash || isAuthRoute) ? '/home' : null;
       }
       if (!isAuthRoute && !isSplash) return '/login';