Improve usage of roles. It should be much easier to read and use now.

common/default.nix

@@ -100,7 +100,5 @@
   security.acme.defaults.email = "zuckerberg@neet.dev";
 
   # Enable Desktop Environment if this is a PC (machine role is "personal")
-  de.enable = (
-    builtins.elem config.networking.hostName config.machines.roles.personal
-  );
+  de.enable = lib.mkDefault (config.thisMachine.hasRole."personal");
 }