fix(nix-hm): launch waybar with invalid GTK_THEME variable

This ensures no borders or stroke are applied — uses purely the CSS
defined for waybar.

config/default.nix

@@ -193,6 +193,7 @@ in {
     };
     services = {
       waybar = {
+        Service.Environment="GTK_THEME='THIS THEME DOES NOT EXIST!'";
         Install.WantedBy = [ "compositor.target" ];
         Unit = {
           PartOf = [ "compositor.target" ];