Improve settings and playback controls

frontend/lib/main.dart

@@ -8,7 +8,7 @@ import 'pages/login_page.dart';
 
 void main() {
   fvp.registerWith();
-  
+
   runApp(
     MultiProvider(
       providers: [
@@ -21,6 +21,8 @@ void main() {
 }
 
 class HightubeApp extends StatelessWidget {
+  const HightubeApp({super.key});
+
   @override
   Widget build(BuildContext context) {
     final auth = context.watch<AuthProvider>();
@@ -42,7 +44,7 @@ class HightubeApp extends StatelessWidget {
           brightness: Brightness.dark,
         ),
       ),
-      themeMode: ThemeMode.system, // 跟随系统切换深浅色
+      themeMode: settings.themeMode,
       home: auth.isAuthenticated ? HomePage() : LoginPage(),
       debugShowCheckedModeBanner: false,
     );