begin migration to dendritic pattern

old-config/modules/display-managers/lightdm.nix

@@ -0,0 +1,11 @@
+{
+  config,
+  pkgs,
+  ...
+}: {
+  services.xserver.enable = true;
+  services.xserver.displayManager.lightdm = {
+    enable = true;
+    greeters.gtk.enable = true;
+  };
+}