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-offline/settings.conf

@@ -0,0 +1,51 @@
+---
+modules-search: [ local ]
+
+sequence:
+    - show:
+        - welcome
+        - locale
+        - keyboard
+        - partition
+        - users
+        - summary
+    - exec:
+        - partition
+        - mount
+        - unpackfs
+        - machineid
+        - fstab
+        - locale
+        - keyboard
+        - localecfg
+        - luksopenswaphookcfg
+        - luksbootkeyfile
+        - initcpiocfg
+        - initcpio
+        - users
+        - displaymanager
+        - networkcfg
+        - hwclock
+        - services-artix
+        - grubcfg
+        - bootloader
+        - postcfg
+        - umount
+    - show:
+        - finished
+
+branding: antergos-next-minimal
+
+prompt-install: false
+
+dont-chroot: false
+
+oem-setup: false
+
+disable-cancel: false
+
+disable-cancel-during-exec: false
+
+hide-back-and-next-during-exec: false
+
+quit-at-end: false