Add KDE and set it as the default on the workstation host

Note: The kde configuration is currently incomplete. It's still missing
some configuration using the plasma-manager flake. I'm going to get
plasma working first and then worry about the small configuration
details.

hosts/workstation/default.nix

@@ -6,8 +6,8 @@
     ./persist.nix
     ../../home/default.nix
 
+    ../../modules/desktop/environments/kde.nix
     ../../modules/system/basic.nix
-    ../../modules/desktop/environments/hyprland.nix
     ../../modules/system/security.nix
     ../../modules/desktop/apps/communication.nix
     ../../modules/desktop/apps/games.nix