fix: configure GDM auto-login for workshop user

- Use GDM-specific autoLogin instead of generic displayManager autoLogin
- Auto-login as workshop user instead of root to properly start GNOME session
- Remove conflicting generic autoLogin from flake.nix
- Keep gnome-terminal sessionCommands for workshop terminal

common.nix

@@ -1214,6 +1214,12 @@ isoConfig
   services.xserver = {
     enable = true;
     desktopManager.gnome.enable = true;
-    displayManager.gdm.enable = true;
+    displayManager.gdm = {
+      enable = true;
+      autoLogin = {
+        enable = true;
+        user = "workshop";
+      };
+    };
   };
 }