[live-usb] Clean up config

Also switched from trying to override the `nixos` user to instead just
installing home-manager _into_ the `nixos` user. It felt a bit like
fighting the tide otherwise.

machines/live-usb/configuration.nix

@@ -11,9 +11,12 @@
   roles = {
     audio.enable = true;
     bluetooth.enable = true;
-    users = {
+    desktop = {
       enable = true;
-      extraGroups = [ "video" "wheel" "networkmanager" ];
+      kde = true;
+      x11 = true;
+      wayland = true;
+      sddm = true;
     };
   };
 
@@ -72,15 +75,6 @@
     };
   };
 
-  # Override default nixos user, set johno as the main user with password
-  users.users.nixos.enable = false;
-  users.users.johno = {
-    isNormalUser = true;
-    description = "John Ogle";  
-    extraGroups = [ "wheel" "networkmanager" "audio" "video" ];
-    password = "nixos";  # Simple password for live environment
-  };
-
   # ISO customization
   isoImage = {
     volumeID = "NIXOS-LIVE";