🚫 feat(web): add 403 Forbidden page and AdminRoute guard

- Add new Forbidden page at /forbidden (`web/src/pages/Forbidden/index.js`)
  - Use Semi-UI Empty with IllustrationNoAccess (250x250)
  - Update i18n description to: '您无权访问此页面，请联系管理员~'
  - Align visual style with existing 404 page
- Introduce `AdminRoute` in `web/src/helpers/auth.js`
  - Use `UserContext`/localStorage; redirect to `/forbidden` when `!user` or `user.role < 10`
- Protect console/admin routes with `AdminRoute` and register `/forbidden` in `web/src/App.js`
- Update `web/src/i18n/locales/en.json`
  - Add English translation for the new forbidden message
  - Remove legacy "没有权限" entry
- Lint passes; no runtime errors observed

web/src/i18n/locales/en.json

@@ -1459,6 +1459,7 @@
   "设计与开发由": "Designed & Developed with love by",
   "演示站点": "Demo Site",
   "页面未找到，请检查您的浏览器地址是否正确": "Page not found, please check if your browser address is correct",
+  "您无权访问此页面，请联系管理员": "You do not have permission to access this page. Please contact the administrator.",
   "New API项目仓库地址：": "New API project repository address: ",
   "© {{currentYear}}": "© {{currentYear}}",
   "| 基于": " | Based on ",