Production-Grade (ish) Rails deployment on Hetzner with Kamal

I've been toying around with Kamal for some time now, and I believe I have come up with a nice setup for a reasonably robust deployment. It includes two servers, one for the application and another for database and caching, a firewall to expose only the ports we need (e.g., the database server is not exposed at all), and automated backups. Let's get down to business.