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)

modules/nixos/openssh/default.nix

@@ -9,7 +9,7 @@ in
     ports = mkDefault [ 2299 ];
     openFirewall = mkDefault true;
     settings = {
-      PermitRootLogin = mkDefault "prohibit-password";
+      PermitRootLogin = mkDefault "no";
       PasswordAuthentication = mkDefault false;
     };
   };