refactor some modules

modules/profiles/xfce4/default.nix

@@ -0,0 +1,18 @@
+{
+  lib,
+  config,
+  ...
+}:
+{
+  imports = [ ../desktop ];
+
+  config = {
+    services.xserver = {
+      desktopManager.xfce.enable = true;
+    };
+
+    services.displayManager = {
+      defaultSession = lib.mkForce "xfce";
+    };
+  };
+}