Fix Gradio static asset 404s: use demo.app instead of mount_gradio_app

mount_gradio_app mounts Gradio as a FastAPI sub-application, which
breaks /_app/immutable/* static file serving on HF Spaces. Instead,
add REST routes directly to Gradio's own FastAPI instance via demo.app.

Co-Authored-By: Oz <oz-agent@warp.dev>

app.py

@@ -632,17 +632,17 @@ The AI assistant is here to help with practical, actionable guidance.
             )
 
 
-# Mount the Gradio Blocks app inside a FastAPI app so we can expose
-# our own REST endpoints (see rest_api.py) alongside the UI.
-from fastapi import FastAPI  # noqa: E402  (kept here so module-level Gradio init runs first)
+# Expose REST endpoints alongside the Gradio UI.
+#
+# Instead of mounting Gradio as a sub-app of FastAPI (which breaks
+# /_app/immutable/* static-file serving on HF Spaces), we add our
+# REST router directly to Gradio's own FastAPI app.  This ensures
+# Gradio's SvelteKit frontend assets are served correctly.
 from rest_api import build_router  # noqa: E402
 
-api = FastAPI(title="Farm Layout Model API")
-api.include_router(build_router())
-
-# `app` is the ASGI entrypoint HF Spaces / uvicorn will serve.
-app = gr.mount_gradio_app(api, demo, path="/")
+demo.queue()
+app = demo.app  # Gradio's internal FastAPI instance
+app.include_router(build_router())  # add /api/v1/* routes
 
 if __name__ == "__main__":
-    import uvicorn
-    uvicorn.run(app, host="0.0.0.0", port=7860)
+    demo.launch(server_name="0.0.0.0", server_port=7860)