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/features/chat/screens/searching_screen.dart

@@ -0,0 +1,55 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_bloc/flutter_bloc.dart';
+import 'package:go_router/go_router.dart';
+import '../../../core/pairing/pairing_bloc.dart';
+
+class SearchingScreen extends StatelessWidget {
+  const SearchingScreen({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return BlocListener<PairingBloc, PairingState>(
+      listener: (context, state) {
+        if (state is PairingBestieFound) {
+          context.go('/chat/found', extra: {
+            'sessionId': state.sessionId,
+            'mitraName': state.mitraName,
+          });
+        } else if (state is PairingNoBestie) {
+          context.go('/chat/no-bestie');
+        } else if (state is PairingCancelled) {
+          context.go('/home');
+        }
+      },
+      child: Scaffold(
+        body: Center(
+          child: Padding(
+            padding: const EdgeInsets.all(32),
+            child: Column(
+              mainAxisAlignment: MainAxisAlignment.center,
+              children: [
+                const CircularProgressIndicator(),
+                const SizedBox(height: 32),
+                const Text(
+                  'Mencari Bestie...',
+                  style: TextStyle(fontSize: 24, fontWeight: FontWeight.bold),
+                ),
+                const SizedBox(height: 8),
+                const Text(
+                  'Tunggu sebentar ya, kami sedang mencarikan Bestie untukmu',
+                  textAlign: TextAlign.center,
+                  style: TextStyle(fontSize: 16, color: Colors.grey),
+                ),
+                const SizedBox(height: 48),
+                OutlinedButton(
+                  onPressed: () => context.read<PairingBloc>().add(CancelPairing()),
+                  child: const Text('Batalkan'),
+                ),
+              ],
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}