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/packagechooser_dm.conf

@@ -0,0 +1,31 @@
+---
+mode: required
+
+method: netinstall-select
+
+labels:
+    step: "Display Manager"
+    step[de]: "Display Manager"
+
+default: SDDM
+
+items:
+    - id: SDDM
+      name: sddm
+      description: "QML-based display manager (KDE default)"
+      screenshot: ""
+
+    - id: LightDM
+      name: lightdm
+      description: "Cross-desktop display manager (GTK)"
+      screenshot: ""
+
+    - id: LXDM
+      name: lxdm
+      description: "Lightweight display manager (LXDE)"
+      screenshot: ""
+
+    - id: LY
+      name: ly
+      description: "Minimal TUI display manager"
+      screenshot: ""