feat: configurable watch together relay server

lib/watch_together/providers/watch_together_provider.dart

@@ -4,6 +4,7 @@ import 'dart:math';
 import 'package:flutter/foundation.dart';
 
 import '../../mpv/mpv.dart';
+import '../../services/settings_service.dart';
 import '../../utils/app_logger.dart';
 import '../models/sync_message.dart';
 import '../models/watch_session.dart';
@@ -189,7 +190,8 @@ class WatchTogetherProvider with ChangeNotifier {
 
     appLogger.d('WatchTogether: Creating session with control mode: $controlMode');
 
-    _peerService = WatchTogetherPeerService();
+    final customRelayUrl = SettingsService.instanceOrNull?.getCustomRelayUrl();
+    _peerService = WatchTogetherPeerService(customBaseUrl: customRelayUrl);
     _setupPeerServiceListeners();
 
     try {
@@ -236,7 +238,8 @@ class WatchTogetherProvider with ChangeNotifier {
 
     appLogger.d('WatchTogether: Joining session: $sessionId');
 
-    _peerService = WatchTogetherPeerService();
+    final customRelayUrl = SettingsService.instanceOrNull?.getCustomRelayUrl();
+    _peerService = WatchTogetherPeerService(customBaseUrl: customRelayUrl);
     _setupPeerServiceListeners();
 
     _session = WatchSession.joinAsGuest(sessionId: sessionId);

lib/watch_together/screens/watch_together_screen.dart

@@ -9,6 +9,7 @@ import 'package:provider/provider.dart';
 import '../../i18n/strings.g.dart';
 import '../../focus/focusable_button.dart';
 import '../../focus/focusable_wrapper.dart';
+import '../../services/settings_service.dart';
 import '../../utils/app_logger.dart';
 import '../../utils/dialogs.dart';
 import '../../utils/snackbar_helper.dart';
@@ -80,10 +81,12 @@ class _NotInSessionViewState extends State<_NotInSessionView> {
   bool _isCreating = false;
   bool _isJoining = false;
   bool? _healthOk;
+  String? _customRelayUrl;
 
   @override
   void initState() {
     super.initState();
+    _customRelayUrl = SettingsService.instanceOrNull?.getCustomRelayUrl();
     _checkHealth();
   }
 
@@ -91,7 +94,7 @@ class _NotInSessionViewState extends State<_NotInSessionView> {
     try {
       final client = HttpClient();
       client.connectionTimeout = const Duration(seconds: 5);
-      final request = await client.getUrl(Uri.parse(WatchTogetherPeerService.healthUrl));
+      final request = await client.getUrl(Uri.parse(WatchTogetherPeerService.healthUrlFor(_customRelayUrl)));
       final response = await request.close().namedTimeout(const Duration(seconds: 5), operation: 'WatchTogether health check');
       final body = await response.transform(const SystemEncoding().decoder).join();
       client.close();

lib/watch_together/services/watch_together_peer_service.dart

@@ -20,9 +20,24 @@ export '../../services/base_peer_service.dart' show PeerError, PeerErrorType;
 /// - Sending/receiving sync messages through the relay server
 /// - Reconnection on WebSocket drops
 class WatchTogetherPeerService with KeepaliveMixin {
-  static const String _baseUrl = 'https://ice.plezy.app';
-  static String get healthUrl => '$_baseUrl/health';
-  static const String _relayUrl = 'wss://ice.plezy.app/relay';
+  static const String defaultBaseUrl = 'https://ice.plezy.app';
+
+  final String _baseUrl;
+
+  static String get healthUrl => '$defaultBaseUrl/health';
+
+  static String healthUrlFor(String? customBaseUrl) {
+    final base = (customBaseUrl != null && customBaseUrl.trim().isNotEmpty) ? customBaseUrl.trim() : defaultBaseUrl;
+    return '$base/health';
+  }
+
+  String get _relayUrl {
+    final wsBase = _baseUrl.replaceFirst(RegExp(r'^https://'), 'wss://').replaceFirst(RegExp(r'^http://'), 'ws://');
+    return '$wsBase/relay';
+  }
+
+  WatchTogetherPeerService({String? customBaseUrl})
+      : _baseUrl = (customBaseUrl != null && customBaseUrl.trim().isNotEmpty) ? customBaseUrl.trim() : defaultBaseUrl;
 
   WebSocketChannel? _channel;
   StreamSubscription? _channelSubscription;