When accessing /static/web-ui without trailing slash, the request would
fail with "RuntimeError: File at path ... is not a file" because:
1. The route /static/web-ui/{file_path:path} doesn't match paths without
trailing slash (Starlette's path regex requires the /)
2. The request falls through to StaticFiles mount, which tries to serve
the directory as a file
This fix:
- Sets html=True on StaticFiles mount to automatically redirect directory
URLs to trailing slash versions
- Adds os.path.isdir() check to handle empty file_path gracefully
Fixes#2680
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
