* Add dynamic subpath support for WebUI
- Add SubpathConfig utility for server-side subpath detection
- Configure React Router basename from server config
- Update API base URL handling for subpath compatibility
- Fix asset loading with relative paths
- Add VITE_SUBPATH environment variable for development
- Update locales and manifest paths for subpath support
Closes#174
* Move VITE_SUBPATH interface to vite-env.d.ts
* Ensure production bundle always uses relative base
