feat: switch desktop environment from XFCE to GNOME

- Change desktopManager from xfce to gnome
- Change displayManager from lightdm to gdm
- Update sessionCommands to use gnome-terminal instead of xfce4-terminal

flake.nix

@@ -120,7 +120,7 @@
               };
               # Keep GUI session commands for when GUI is used
               services.xserver.displayManager.sessionCommands = ''
-                ${pkgs.xfce.xfce4-terminal}/bin/xfce4-terminal --fullscreen --maximize --hide-toolbar --hide-borders --hide-menubar --hide-toolbar --title="Workshop Terminal" &
+                ${pkgs.gnome-terminal}/bin/gnome-terminal --full-screen --title="Workshop Terminal" &
               '';
             }
           )