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/grubcfg.conf

@@ -0,0 +1,20 @@
+# SPDX-FileCopyrightText: no
+# SPDX-License-Identifier: CC0-1.0
+---
+overwrite: false
+
+prefer_grub_d: false
+
+keep_distributor: false
+
+kernel_params: [ "quiet" ]
+
+defaults:
+    GRUB_TIMEOUT: 5
+    GRUB_DEFAULT: "saved"
+    GRUB_DISABLE_SUBMENU: true
+    GRUB_TERMINAL_OUTPUT: "console"
+    GRUB_DISABLE_RECOVERY: true
+    GRUB_THEME: "/usr/share/grub/themes/antergos/theme.txt"
+
+always_use_defaults: false