feat: 移除 H5ShellPage 中的多余媒体控制逻辑；优化 ShellBranding 加载方式

lib/config/app_config.dart

@@ -45,14 +45,6 @@ class AppConfig {
         .toString();
   }
 
-  static String withFreshShellCacheBust(String url) {
-    final uri = Uri.parse(url);
-    final queryParameters = Map<String, String>.from(uri.queryParameters)
-      ..['shell_cache_bust'] = DateTime.now().millisecondsSinceEpoch.toString();
-
-    return uri.replace(queryParameters: queryParameters).toString();
-  }
-
   static String _normalizeHomeUrl(String host) {
     final value = host.trim();
     final normalized =