Replace native Twilio Voice SDK with WebView-based softphone

Rewrites the mobile app from a native Twilio Voice SDK integration
(Android Telecom/ConnectionService) to a thin WebView shell that loads
a standalone browser phone page from WordPress. This eliminates the
buggy Android phone account registration, fixes frequent logouts by
using 7-day WP session cookies instead of JWT tokens, and maintains
all existing call features (dialpad, queues, hold, transfer, requeue,
recording, caller ID, agent status).

Server-side:
- Add class-twp-mobile-phone-page.php: standalone /twp-phone/ endpoint
  with mobile-optimized UI, dark mode, tab navigation, and Flutter
  WebView JS bridge
- Extend auth cookie to 7 days for phone agents
- Add WP AJAX handler for FCM token registration (cookie auth)

Flutter app (v2.0.0):
- Replace 18 native files with 5-file WebView shell
- Login via wp-login.php in WebView (auto-detect redirect on success)
- Full-screen WebView with auto microphone grant for WebRTC
- FCM push notifications preserved for queue alerts
- Remove: twilio_voice, dio, provider, JWT auth, SSE, native call UI

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

mobile/lib/app.dart

@@ -1,11 +1,7 @@
 import 'package:flutter/material.dart';
-import 'package:provider/provider.dart';
-import 'services/api_client.dart';
-import 'providers/auth_provider.dart';
-import 'providers/agent_provider.dart';
-import 'providers/call_provider.dart';
+import 'package:flutter_secure_storage/flutter_secure_storage.dart';
 import 'screens/login_screen.dart';
-import 'screens/dashboard_screen.dart';
+import 'screens/phone_screen.dart';
 
 class TwpSoftphoneApp extends StatefulWidget {
   const TwpSoftphoneApp({super.key});
@@ -15,51 +11,77 @@ class TwpSoftphoneApp extends StatefulWidget {
 }
 
 class _TwpSoftphoneAppState extends State<TwpSoftphoneApp> {
-  final _apiClient = ApiClient();
+  static const _storage = FlutterSecureStorage();
+  String? _serverUrl;
+  bool _loading = true;
+
+  @override
+  void initState() {
+    super.initState();
+    _checkSavedSession();
+  }
+
+  Future<void> _checkSavedSession() async {
+    final url = await _storage.read(key: 'server_url');
+    if (mounted) {
+      setState(() {
+        _serverUrl = url;
+        _loading = false;
+      });
+    }
+  }
+
+  void _onLoginSuccess(String serverUrl) {
+    setState(() {
+      _serverUrl = serverUrl;
+    });
+  }
+
+  void _onLogout() async {
+    await _storage.delete(key: 'server_url');
+    if (mounted) {
+      setState(() {
+        _serverUrl = null;
+      });
+    }
+  }
+
+  void _onSessionExpired() {
+    // Server URL is still saved, but session cookie is gone.
+    // Show login screen but keep the server URL pre-filled.
+    if (mounted) {
+      setState(() {
+        _serverUrl = null;
+      });
+    }
+  }
 
   @override
   Widget build(BuildContext context) {
-    return ChangeNotifierProvider(
-      create: (_) {
-        final auth = AuthProvider(_apiClient);
-        auth.tryRestoreSession();
-        return auth;
-      },
-      child: MaterialApp(
-        title: 'TWP Softphone',
-        debugShowCheckedModeBanner: false,
-        theme: ThemeData(
-          colorSchemeSeed: Colors.blue,
-          useMaterial3: true,
-          brightness: Brightness.light,
-        ),
-        darkTheme: ThemeData(
-          colorSchemeSeed: Colors.blue,
-          useMaterial3: true,
-          brightness: Brightness.dark,
-        ),
-        home: Consumer<AuthProvider>(
-          builder: (context, auth, _) {
-            if (auth.state == AuthState.authenticated) {
-              return MultiProvider(
-                providers: [
-                  ChangeNotifierProvider(
-                    create: (_) => AgentProvider(
-                      auth.apiClient,
-                      auth.sseService,
-                    )..refresh(),
-                  ),
-                  ChangeNotifierProvider(
-                    create: (_) => CallProvider(auth.voiceService),
-                  ),
-                ],
-                child: const DashboardScreen(),
-              );
-            }
-            return const LoginScreen();
-          },
-        ),
+    return MaterialApp(
+      title: 'TWP Softphone',
+      debugShowCheckedModeBanner: false,
+      theme: ThemeData(
+        colorSchemeSeed: Colors.blue,
+        useMaterial3: true,
+        brightness: Brightness.light,
       ),
+      darkTheme: ThemeData(
+        colorSchemeSeed: Colors.blue,
+        useMaterial3: true,
+        brightness: Brightness.dark,
+      ),
+      home: _loading
+          ? const Scaffold(
+              body: Center(child: CircularProgressIndicator()),
+            )
+          : _serverUrl != null
+              ? PhoneScreen(
+                  serverUrl: _serverUrl!,
+                  onLogout: _onLogout,
+                  onSessionExpired: _onSessionExpired,
+                )
+              : LoginScreen(onLoginSuccess: _onLoginSuccess),
     );
   }
 }