feat: add Antergos NeXT Minimal (Xfce) profile — lightweight ISO edition

Introduces iso-profiles/antergos-minimal/, a new Xfce-based profile for
building a lightweight Antergos NeXT ISO under the 2 GB GitHub Releases
limit (the full Plasma profile produces ~2.15 GB).

Profile structure:
- profile.yaml: Xfce4 desktop, dinit-only init packages, Falkon browser,
  minimal app selection, antergos-xfce-theme included in rootfs
- root-overlay/: SDDM configured for xfce.desktop, GRUB theme pointed to
  antergos, xfconf settings for Antergos-NeXT GTK/xfwm4 theme
- live-overlay/: Calamares offline + online configs, netinstall with
  multiple DE options (Plasma, Xfce, Cinnamon, MATE, LXQt, i3, Sway,
  Hyprland), notesqml@minimal-info step explaining the edition rationale,
  basestrap operations for antergos-release/grub-theme/keyring, display
  manager selection (SDDM/LightDM/LXDM/LY), audio services (pipewire),
  and antergos-xfce-theme in the Xfce subgroup

Default Xfce theme is set to Antergos-NeXT (Numix-derived, blue accent)
via xfconf XML in both live-overlay and root-overlay skel directories.

iso-profiles/antergos-minimal/root-overlay/etc/sddm.conf.d/kde_settings.conf

@@ -0,0 +1,17 @@
+[Autologin]
+Relogin=false
+Session=xfce.desktop
+User=antergos
+
+[General]
+HaltCommand=/usr/bin/loginctl poweroff
+RebootCommand=/usr/bin/loginctl reboot
+
+[Theme]
+Current=breeze
+CursorTheme=breeze_cursors
+Font=Noto Sans,10,-1,0,50,0,0,0,0,0
+
+[Users]
+MaximumUid=60000
+MinimumUid=1000