Allows serving the UI under a subpath (e.g. /ui) instead of root.
- Vite config reads BASE_PATH env var, sets it as the asset base
and injects __BASE_PATH__ for runtime use
- React Router uses basename from __BASE_PATH__ for client-side routing
- Nginx config uses ${BASE_PATH} placeholder, replaced at build time
- Dockerfile accepts BASE_PATH build arg (default: /)
- Woodpecker docker pipeline passes BASE_PATH=/ui