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-online/modules/basestrap.conf

@@ -0,0 +1,36 @@
+---
+backend: pacman
+
+pacman:
+    num_retries: 0
+    disable_download_timeout: false
+    needed_only: false
+    handle_keyrings: true
+    copy_pacconf: true
+    requirements:
+      - dest: /etc
+        mode: "0o755"
+      - dest: /var
+        mode: "0o755"
+      - dest: /var/cache
+        mode: "0o755"
+      - dest: /var/cache/pacman
+        mode: "0o755"
+      - dest: /var/cache/pacman/pkg
+        mode: "0o755"
+      - dest: /var/lib
+        mode: "0o755"
+      - dest: /var/lib/pacman
+        mode: "0o755"
+    keyrings:
+      - artix
+      - antergos-next
+
+base_init: elogind
+
+operations:
+  - install:
+    - base
+    - antergos-next-keyring
+    - antergos-release
+    - antergos-grub-theme