Use `demo` as Gradio entrypoint identifier

- Rename Gradio Blocks context in `src/app.py` from `iface` to `demo` to match official docs
- Update root-level `app.py` wrapper to import and launch `demo` instead of `iface`

src/app.py

@@ -37,4 +37,4 @@ with gr.Blocks() as demo:
     inp.submit(fn=map_symptoms, inputs=inp, outputs=out)
 
 if __name__ == "__main__":
-    demo.launch(server_name="0.0.0.0", server_port=7860)
+    demo.launch(server_name="0.0.0.0", server_port=7860, mcp_server=True)