feat: switch to Gunicorn for production

docker-compose.yml

@@ -11,6 +11,7 @@ services:
     environment:
       - FLASK_APP=main.py
       - FLASK_ENV=production
+      - GUNICORN_CMD_ARGS=--workers=4 --bind=0.0.0.0:5000 --timeout=120
     restart: unless-stopped
     healthcheck:
       test: ["CMD", "curl", "-f", "http://localhost:5000"]