fix(hf-space): fix static dir path for SPA catch-all route

Path(__file__).parent.parent resolves to /app in the container
(/app/app/main.py -> /app/app -> /app), so /app/static is found
correctly and the React SPA catch-all route gets registered.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/main.py

@@ -34,7 +34,7 @@ app.add_middleware(
 )
 app.mount("/media", StaticFiles(directory=settings.storage_dir), name="media")
 
-_STATIC_DIR = Path(__file__).parent.parent.parent / "static"
+_STATIC_DIR = Path(__file__).parent.parent / "static"
 if _STATIC_DIR.is_dir():
     app.mount("/assets", StaticFiles(directory=_STATIC_DIR / "assets"), name="frontend-assets")