refactor: seperate desktop modules

modules/nixos/desktop/ly.nix

@@ -0,0 +1,10 @@
+{
+  flake.modules.nixos.desktop = {
+    services.displayManager.ly = {
+      enable = true;
+      settings = {
+        session_log = "null";
+      };
+    };
+  };
+}