feat(terra): replace tuigreet with a quickshell greeter

greetd now runs a throwaway Hyprland hosting dotfiles/quickshell/greeter.qml,
configured per host via homelab.greeter.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

services/desktop/desktop-hyprland.nix

@@ -2,18 +2,14 @@
 
 # Hyprland (wayland) desktop: compositor, login manager, audio, portals.
 {
+  imports = [ ./quickshell-greeter.nix ];
+
   programs.hyprland.enable = true;
 
   services.gnome.gnome-keyring.enable = true;
   security.pam.services.login.enableGnomeKeyring = true;
   security.pam.services.greetd.enableGnomeKeyring = true;
 
-  services.greetd = {
-    enable = true;
-    settings.default_session.command =
-      "${pkgs.tuigreet}/bin/tuigreet --time --cmd start-hyprland";
-  };
-
   # Audio (pipewire replaces pulseaudio/jack).
   security.rtkit.enable = true;
   services.pipewire = {