fix: prevent port conflict in HF Spaces dev mode

Dev mode spawns CMD multiple times on restart, causing EADDRINUSE.
Wrap uvicorn in a start script that kills any prior instance first.

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

Dockerfile

@@ -56,4 +56,4 @@ EXPOSE 7860
 
 # Run the application from backend directory
 WORKDIR /app/backend
-CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "7860"]
+CMD ["bash", "start.sh"]

backend/start.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+# Entrypoint for HF Spaces dev mode compatibility.
+# Dev mode may spawn the CMD multiple times; kill any prior
+# uvicorn instance so the new one can bind the port.
+pkill -f "uvicorn main:app" 2>/dev/null || true
+sleep 0.3
+exec uvicorn main:app --host 0.0.0.0 --port 7860