(config) Harden Docker deployment for remote servers

Run the Django control panel with Gunicorn instead of the development
runserver and serve static files through WhiteNoise.

Add restart policies, healthchecks, .env-driven production settings, and
a sample .env file for single-server deployments. Update the Docker
entrypoint to collect static assets and document the remote server
deployment and update flow in the README.

Dockerfile

@@ -24,4 +24,4 @@ RUN chmod +x ./scripts/docker-entrypoint
 EXPOSE 8000
 
 ENTRYPOINT ["./scripts/docker-entrypoint"]
-CMD ["python", "manage.py", "runserver", "0.0.0.0:8000"]
+CMD ["gunicorn", "pobsync_server.wsgi:application", "--bind", "0.0.0.0:8000", "--workers", "2", "--timeout", "120"]