feat(bootstrap): add desktop environment support with configurable DE, DM, and display target

roles/global_defaults/defaults/main.yml

@@ -135,6 +135,12 @@ system_defaults:
       user: "_aur_builder"
     chroot:
       tool: "arch-chroot" # arch-chroot|chroot|systemd-nspawn
+    initramfs:
+      generator: "" # auto-detected; override: dracut|mkinitcpio|initramfs-tools
+    desktop:
+      enabled: false
+      environment: ""       # gnome|kde|xfce|sway|hyprland|cinnamon|mate|lxqt|budgie
+      display_manager: ""   # auto from environment when empty; override: gdm|sddm|lightdm|greetd
 
 # Per-hypervisor required fields — drives data-driven validation.
 # All virtual types additionally require network bridge or interfaces.