use gunicorn for prod api

.build/prod/api.Dockerfile

@@ -1,10 +1,10 @@
 FROM python:3.9.20-slim-bookworm
 
-RUN pip install python-dotenv flask
+RUN pip install python-dotenv flask gunicorn
 RUN apt-get update && apt-get install -y curl && apt-get clean && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /app
 COPY api.py tx.sh .
 RUN chmod +x tx.sh api.py
 
-CMD ./api.py
+CMD gunicorn --workers 4 --bind 0.0.0.0:5000 api:app