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/providers/settings_provider.dart

@@ -1,12 +1,13 @@
 import 'package:flutter/material.dart';
 import 'package:shared_preferences/shared_preferences.dart';
-
 class SettingsProvider with ChangeNotifier {
   // Default server address for local development.
   // Using 10.0.2.2 for Android emulator or localhost for Desktop.
   String _baseUrl = "http://localhost:8080";
-  
+  Color _themeColor = Colors.blue;
+
   String get baseUrl => _baseUrl;
+  Color get themeColor => _themeColor;
 
   SettingsProvider() {
     _loadSettings();
@@ -15,6 +16,10 @@ class SettingsProvider with ChangeNotifier {
   void _loadSettings() async {
     final prefs = await SharedPreferences.getInstance();
     _baseUrl = prefs.getString('baseUrl') ?? _baseUrl;
+    final colorValue = prefs.getInt('themeColor');
+    if (colorValue != null) {
+      _themeColor = Color(colorValue);
+    }
     notifyListeners();
   }
 
@@ -24,7 +29,14 @@ class SettingsProvider with ChangeNotifier {
     await prefs.setString('baseUrl', url);
     notifyListeners();
   }
-  
+
+  void setThemeColor(Color color) async {
+    _themeColor = color;
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setInt('themeColor', color.value);
+    notifyListeners();
+  }
+
   // Also provide the RTMP URL based on the same hostname
   String get rtmpUrl {
     final uri = Uri.parse(_baseUrl);