add kitty as required for default hyprland config

modules/nixos/desktop-environment/default.nix

@@ -87,6 +87,12 @@ in {
         libgnome-keyring
       ];
     })
+    (lib.mkIf cfg.hyprland.enable {
+      programs.hyprland.enable = true; # enable Hyprland
+      environment.systemPackages = with pkgs; [
+        pkgs.kitty # required for the default Hyprland config
+      ];
+    })
   ];
 
 }