feat(app-expo): env variants, local iOS prebuild, and About diagnostics

Align staging/production builds with APP_VARIANT bundle IDs, allow staging HTTP on iOS, add ios-prebuild scripts for TestFlight, and show connected API URL on About for non-production builds.

Co-authored-by: Cursor <cursoragent@cursor.com>

app-expo/scripts/use-env.js

@@ -2,7 +2,7 @@
  * 将 app-expo/.env.<name> 复制为 .env，供 Metro/Expo 读取 EXPO_PUBLIC_*。
  *
  * 参数 name → 源文件：
- *   development → .env.development（本地默认：npm start / prestart）
+ *   development → .env.development（仓库已提交；npm start / prestart 默认）
  *   staging     → .env.staging
  *   production  → .env.production
  *