feat: implement chat history, theme customization, and password management

- Added chat history persistence for active rooms with auto-cleanup on stream end.
- Overhauled Settings page with user profile, theme color picker, and password change.
- Added backend API for user password updates.
- Integrated flutter_launcher_icons and updated app icon to 'H' logo.
- Fixed 'Duplicate keys' bug in danmaku by using UniqueKey and filtering historical messages.
- Updated version to 1.0.0-beta3.5 and author info.

frontend/lib/main.dart

@@ -24,21 +24,21 @@ class HightubeApp extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final auth = context.watch<AuthProvider>();
+    final settings = context.watch<SettingsProvider>();
 
     return MaterialApp(
       title: 'Hightube',
-      // 设置深色主题为主，更符合视频类应用的审美
       theme: ThemeData(
         useMaterial3: true,
         colorScheme: ColorScheme.fromSeed(
-          seedColor: Colors.deepPurple,
+          seedColor: settings.themeColor,
           brightness: Brightness.light,
         ),
       ),
       darkTheme: ThemeData(
         useMaterial3: true,
         colorScheme: ColorScheme.fromSeed(
-          seedColor: Colors.deepPurple,
+          seedColor: settings.themeColor,
           brightness: Brightness.dark,
         ),
       ),