fix: remove duplicate ai-worker user definition in configuration.nix

ai-worker is now defined in users/ai-worker/ai-worker.nix module

hosts/uconsole-cm5/configuration.nix

@@ -20,16 +20,8 @@
     users.ai-worker.main
   ];
 
-  # AI worker user (Hermes SSH access)
+  # Gitsign: sign git commits with age identity
-  users.users.ai-worker = {
+  programs.gitsign.enable = true;
-    isNormalUser = false;
-    shell = pkgs.bash;
-    openssh.authorizedKeys.keys = with keys; [
-      users.ai-worker.main
-    ];
-  };
-
-  # Age secret for gortium password (file created by user)
   age.secrets.gortium_password = {
     file = ../secrets/gortium_password.age;
   };