fix: 修复 Flutter Web 生产环境 API 地址未生效的问题

- NetworkConfig.baseUrl 改为使用 ApiEndpoints.baseUrl
- 确保构建时 --dart-define=ENV=prod 能正确切换环境

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: "3100103420" /* Flutter's service worker is deprecated and will be removed in a future Flutter release. */
+    serviceWorkerVersion: "2084931057" /* Flutter's service worker is deprecated and will be removed in a future Flutter release. */
   }
 });