fix: 修复 Flutter Web 白屏问题

- main.dart: 添加全局错误处理和 FlutterError.onError
- index.html: 添加加载指示器，vconsole 仅在开发环境启用
- dio_client.dart: 添加详细错误日志，优化超时配置

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

flutter_monisuo/build/web/flutter_bootstrap.js

@@ -37,6 +37,6 @@ _flutter.buildConfig = {"engineRevision":"e4b8dca3f1b4ede4c30371002441c88c12187e
 
 _flutter.loader.load({
   serviceWorkerSettings: {
-    serviceWorkerVersion: "2873482940" /* Flutter's service worker is deprecated and will be removed in a future Flutter release. */
+    serviceWorkerVersion: "1409326861" /* Flutter's service worker is deprecated and will be removed in a future Flutter release. */
   }
 });