replace deploy-rs CI with Comin pull-based deployment

- Add Comin service for cryodev-main (polls git repo, auto-deploys)
- Fix cryodev-pi Comin URL (cryodev-server.git -> cryodev.git)
- Remove deploy-rs from CI pipeline (was insecure with shared runner)
- Remove deploy SSH key, root SSH login, sudo rules for gitea-runner
- Revert PermitRootLogin back to 'no'
- CI now only runs flake-check + build (no deploy)
- Deployment happens via Comin (both hosts poll and self-deploy)

flake.nix

@@ -127,8 +127,6 @@
             sshOpts = [
               "-p"
               "2299"
-              "-o"
-              "StrictHostKeyChecking=accept-new"
             ];
             profiles.system = {
               user = "root";