feat: 重构环境配置，移除 openim_common 依赖并优化主页 URL 获取逻辑

lib/config/app_config.dart

@@ -1,8 +1,18 @@
-import 'package:openim_common/openim_common.dart' as openim_common;
+enum Environment {
+  production,
+}
 
 class AppConfig {
+  static const Environment currentEnvironment = Environment.production;
+
+  static final Map<Environment, List<String>> _environmentHosts = {
+    Environment.production: [
+      'h5-im.imharry.work',
+    ],
+  };
+
   static List<String> get environmentHosts {
-    return openim_common.Config.environmentHosts;
+    return _environmentHosts[currentEnvironment] ?? const [];
   }
 
   static String get homeUrl {