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/core/pairing/pairing_notifier.dart

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+import 'dart:async';
+import 'dart:convert';
+import 'package:dio/dio.dart';
+import 'package:firebase_auth/firebase_auth.dart';
+import 'package:riverpod_annotation/riverpod_annotation.dart';
+import 'package:web_socket_channel/web_socket_channel.dart';
+import '../api/api_client.dart';
+import '../api/api_client_provider.dart';
+import '../constants.dart';
+
+part 'pairing_notifier.g.dart';
+
+// States
+sealed class PairingData {
+  const PairingData();
+}
+
+class PairingInitialData extends PairingData {
+  const PairingInitialData();
+}
+
+class PairingSearchingData extends PairingData {
+  final String sessionId;
+  const PairingSearchingData(this.sessionId);
+}
+
+class PairingBestieFoundData extends PairingData {
+  final String sessionId;
+  final String mitraName;
+  const PairingBestieFoundData({required this.sessionId, required this.mitraName});
+}
+
+class PairingActiveData extends PairingData {
+  final String sessionId;
+  final String mitraName;
+  const PairingActiveData({required this.sessionId, required this.mitraName});
+}
+
+class PairingNoBestieData extends PairingData {
+  const PairingNoBestieData();
+}
+
+class PairingCancelledData extends PairingData {
+  const PairingCancelledData();
+}
+
+class PairingErrorData extends PairingData {
+  final String message;
+  const PairingErrorData(this.message);
+}
+
+@Riverpod(keepAlive: true)
+class Pairing extends _$Pairing {
+  Timer? _timeoutTimer;
+  WebSocketChannel? _channel;
+  StreamSubscription? _wsSubscription;
+
+  ApiClient get _apiClient => ref.read(apiClientProvider);
+
+  @override
+  PairingData build() => const PairingInitialData();
+
+  Future<void> requestPairing() async {
+    await _doPairingRequest({});
+  }
+
+  Future<void> requestPairingWithTier({int? durationMinutes, int? price, bool isFreeTrial = false}) async {
+    final body = <String, dynamic>{};
+    if (isFreeTrial) {
+      body['is_free_trial'] = true;
+    } else {
+      body['duration_minutes'] = durationMinutes;
+      body['price'] = price;
+    }
+    await _doPairingRequest(body);
+  }
+
+  Future<void> _doPairingRequest(Map<String, dynamic> body) async {
+    if (state is! PairingInitialData) {
+      state = const PairingInitialData();
+    }
+    try {
+      await _connectWebSocket();
+
+      final response = await _apiClient.post('/api/client/chat/request', data: body);
+      final data = response['data'] as Map<String, dynamic>;
+      final sessionId = data['id'] as String;
+
+      state = PairingSearchingData(sessionId);
+
+      _timeoutTimer = Timer(const Duration(seconds: 60), () {
+        _cleanup();
+        state = const PairingNoBestieData();
+      });
+    } on DioException catch (e) {
+      _cleanup();
+      final code = e.response?.data?['error']?['code'];
+      if (code == 'NO_MITRA_AVAILABLE') {
+        state = const PairingNoBestieData();
+      } else if (code == 'ALREADY_ACTIVE') {
+        state = const PairingErrorData('Kamu sudah memiliki sesi aktif.');
+      } else if (code == 'FREE_TRIAL_INELIGIBLE') {
+        state = const PairingErrorData('Kamu tidak memenuhi syarat untuk free trial.');
+      } else {
+        state = const PairingErrorData('Gagal memulai. Coba lagi.');
+      }
+    }
+  }
+
+  Future<void> _connectWebSocket() async {
+    _closeWebSocket();
+    final user = FirebaseAuth.instance.currentUser;
+    if (user == null) return;
+
+    final token = await user.getIdToken();
+    final wsUrl = ApiClient.baseUrl
+        .replaceFirst('https://', 'wss://')
+        .replaceFirst('http://', 'ws://');
+
+    _channel = WebSocketChannel.connect(Uri.parse('$wsUrl/api/shared/ws'));
+
+    _wsSubscription = _channel!.stream.listen(
+      (raw) {
+        final data = jsonDecode(raw as String) as Map<String, dynamic>;
+        if (data['type'] == WsMessage.authOk) return;
+        _onStatusUpdate(data);
+      },
+      onError: (_) {},
+      onDone: () {},
+    );
+
+    _channel!.sink.add(jsonEncode({
+      'type': WsMessage.auth,
+      'token': token,
+    }));
+  }
+
+  Future<void> _onStatusUpdate(Map<String, dynamic> data) async {
+    final type = data['type'] as String?;
+
+    if (type == WsMessage.paired) {
+      _cleanup();
+      final mitraName = data['mitra_display_name'] as String? ?? 'Bestie';
+      final sessionId = data['session_id'] as String;
+      state = PairingBestieFoundData(sessionId: sessionId, mitraName: mitraName);
+
+      await Future.delayed(const Duration(seconds: 2));
+      state = PairingActiveData(sessionId: sessionId, mitraName: mitraName);
+    } else if (type == SessionStatus.expired) {
+      _cleanup();
+      state = const PairingNoBestieData();
+    }
+  }
+
+  Future<void> cancelPairing() async {
+    if (state is PairingSearchingData) {
+      final sessionId = (state as PairingSearchingData).sessionId;
+      try {
+        await _apiClient.post('/api/client/chat/request/$sessionId/cancel');
+      } catch (_) {}
+      _cleanup();
+      state = const PairingCancelledData();
+    }
+  }
+
+  void reset() {
+    _cleanup();
+    state = const PairingInitialData();
+  }
+
+  void _closeWebSocket() {
+    _wsSubscription?.cancel();
+    _wsSubscription = null;
+    _channel?.sink.close();
+    _channel = null;
+  }
+
+  void _cleanup() {
+    _timeoutTimer?.cancel();
+    _timeoutTimer = null;
+    _closeWebSocket();
+  }
+}

client_app/lib/core/pairing/pairing_notifier.g.dart

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+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'pairing_notifier.dart';
+
+// **************************************************************************
+// RiverpodGenerator
+// **************************************************************************
+
+String _$pairingHash() => r'93049804c1d55a0195a56b97d6e7f34fe6ab8086';
+
+/// See also [Pairing].
+@ProviderFor(Pairing)
+final pairingProvider = NotifierProvider<Pairing, PairingData>.internal(
+  Pairing.new,
+  name: r'pairingProvider',
+  debugGetCreateSourceHash:
+      const bool.fromEnvironment('dart.vm.product') ? null : _$pairingHash,
+  dependencies: null,
+  allTransitiveDependencies: null,
+);
+
+typedef _$Pairing = Notifier<PairingData>;
+// ignore_for_file: type=lint
+// ignore_for_file: subtype_of_sealed_class, invalid_use_of_internal_member, invalid_use_of_visible_for_testing_member, deprecated_member_use_from_same_package