move deploy key to host config, add ralph and benjamin users

- Move forgejo-deploy pubkey from users/steffen to hosts/cryodev-main/
  (deploy key belongs to the host, not a user)
- Remove deploy key from steffen's authorized keys
- Add users ralph and benjamin (pubkeys pending)
- Register both new users in cryodev-main host config

hosts/cryodev-main/deploy-key.pub

@@ -0,0 +1 @@
+ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFIPGMqOV+YrGle8X7/hctW4Sha/bzeTsTP9AcDN9bA2 forgejo-deploy

hosts/cryodev-main/services/openssh.nix

@@ -12,6 +12,6 @@
 
   # Root SSH key for deploy-rs (key-only, no password)
   users.users.root.openssh.authorizedKeys.keyFiles = [
-    ../../../users/steffen/pubkeys/forgejo-deploy.pub
+    ../deploy-key.pub
   ];
 }

hosts/cryodev-main/users.nix

@@ -4,5 +4,7 @@
   imports = [
     outputs.nixosModules.normalUsers
     ../../users/steffen
+    ../../users/ralph
+    ../../users/benjamin
   ];
 }