Add runtime microphone permission request for WebRTC calls

The RECORD_AUDIO permission was declared in the manifest but never
requested at runtime, causing WebRTC to fail on Android 6+. Now
requests microphone permission on app startup before initializing
the WebView.

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

mobile/lib/screens/phone_screen.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:permission_handler/permission_handler.dart';
 import 'package:webview_flutter/webview_flutter.dart';
 import 'package:webview_flutter_android/webview_flutter_android.dart';
 import '../services/push_notification_service.dart';
@@ -40,6 +41,15 @@ class _PhoneScreenState extends State<PhoneScreen> with WidgetsBindingObserver {
     super.initState();
     WidgetsBinding.instance.addObserver(this);
     _pushService = PushNotificationService();
+    _requestPermissionsAndInit();
+  }
+
+  Future<void> _requestPermissionsAndInit() async {
+    // Request microphone permission before initializing WebView
+    final micStatus = await Permission.microphone.request();
+    if (micStatus.isDenied || micStatus.isPermanentlyDenied) {
+      debugPrint('TWP: Microphone permission denied: $micStatus');
+    }
     _initWebView();
     _initPush();
   }