Fix /museum 404: attach routes to the real served FastAPI app

Fix ZeroGPU: back to demo.launch(), redirect root to /museum

Serve 3D museum at root, mount Gradio at /create

fix: demo.launch(ssr_mode=False) — prevents Node.js SSR from competing for port 7860

fix: back to mount_gradio_app+uvicorn — spaces.GPU now present, port conflict resolved

fix: threading.Event().wait() to block main thread in Gradio 6.x

fix: css to launch(), ssr_mode=False — avoid Node.js crash

fix: use demo.launch() — single server entry for sdk:gradio

Initial Gradio Space — Dream Museum