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/calamares/modules/images/s6.svg

@@ -0,0 +1,6 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64">
+  <circle cx="32" cy="32" r="30" fill="#9b59b6"/>
+  <g transform="translate(21,21) scale(1)">
+    <path d="m11 3a8 8 0 0 0-7.9277344 7h1.0058594a7 7 0 0 1 6.921875-6 7 7 0 0 1 6.320312 4h-3.320312v1h5v-1-4h-1v3.1679688a8 8 0 0 0-7-4.1679688zm6.921875 9a7 7 0 0 1-6.921875 6 7 7 0 0 1-6.3105469-4h3.3105469v-1h-5v1 4h1v-3.195312a8 8 0 0 0 7 4.195312 8 8 0 0 0 7.927734-7h-1.005859z" fill="white"/>
+  </g>
+</svg>