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/live-overlay/etc/issue

@@ -0,0 +1,19 @@
+[?25l[?7l              `.-/::/-``
+            .-/osssssssso/.
+           :osyysssssssyyys+-
+        `.+yyyysssssssssyyyyy+.
+       `/syyyyyssssssssssyyyyys-`
+      `/yhyyyyysss++ssosyyyyhhy/`
+     .ohhhyyyyso++/+oso+syy+shhhho.
+    .shhhhysoo++//+sss+++yyy+shhhhs.
+   -yhhhhs+++++++ossso+++yyys+ohhddy:
+  -yddhhyo+++++osyyss++++yyyyooyhdddy-
+ .yddddhso++osyyyyys+++++yyhhsoshddddy`
+`odddddhyosyhyyyyyy++++++yhhhyosddddddo
+.dmdddddhhhhhhhyyyo+++++shhhhhohddddmmh.
+ddmmdddddhhhhhhhso++++++yhhhhhhdddddmmdy
+dmmmdddddddhhhyso++++++shhhhhddddddmmmmh
+-dmmmdddddddhhyso++++oshhhhdddddddmmmmd-
+.smmmmddddddddhhhhhhhhhdddddddddmmmms.
+   `+ydmmmdddddddddddddddddddmmmmdy/.
+      `.:+ooyyddddddddddddyyso+:.`