Finish the DeployHQ cutover

GitHub Actions deploys are working, but DeployHQ is still running, still deploying to the live site, and still being paid for. The migration is stuck halfway.

Tracked as issue #38.

Remaining steps

1. Confirm the new box actually renders. Right now all that's been proven is that files land and rsync exits zero. Nobody has loaded the site and looked at it.
2. Give the new server its own database. It's currently borrowing the live production one, which means there are two live copies of the same data.
3. Repoint DNS.
4. Switch DeployHQ off.

Step 1 is the one to do first, and it's five minutes. Everything after it depends on the answer.

Step 2 is the one carrying real risk while it stays undone.