Phase 2 scaffold: mitra online status & pairing logic

Add mitra online/offline status with heartbeat-based auto-offline,
customer-mitra pairing via Valkey pub/sub blast, session management,
and control center dashboard with real-time stats.

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

client_app/lib/main.dart

@@ -3,6 +3,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'core/api/api_client.dart';
 import 'core/auth/auth_bloc.dart';
+import 'core/pairing/pairing_bloc.dart';
 import 'firebase_options.dart';
 import 'router.dart';
 
@@ -17,8 +18,13 @@ class App extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return BlocProvider(
-      create: (_) => AuthBloc(apiClient: ApiClient())..add(AppStarted()),
+    final apiClient = ApiClient();
+    return MultiBlocProvider(
+      providers: [
+        BlocProvider(create: (_) => AuthBloc(apiClient: apiClient)..add(AppStarted())),
+        BlocProvider(create: (_) => PairingBloc(apiClient: apiClient)),
+        RepositoryProvider.value(value: apiClient),
+      ],
       child: BlocBuilder<AuthBloc, AuthState>(
         builder: (context, state) {
           return MaterialApp.router(