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/partition.conf

@@ -0,0 +1,32 @@
+efi:
+    mountPoint:         "/boot/efi"
+    recommendedSize:    512MiB
+    minimumSize:        256MiB
+    label:              "EFI"
+
+userSwapChoices:
+    - none      # Create no swap, use no swap
+    - small     # Up to 4GB
+    - suspend   # At least main memory size
+    - file      # To swap file instead of partition
+
+swapPartitionName:      swap
+
+luksGeneration: luks1
+
+drawNestedPartitions:   true
+
+alwaysShowPartitionLabels: true
+
+initialPartitioningChoice: none
+
+initialSwapChoice: suspend
+
+defaultPartitionTableType: msdos
+
+requiredPartitionTableType:
+    - msdos
+    - gpt
+
+defaultFileSystemType:  "ext4"
+availableFileSystemTypes:  ["ext4","btrfs","f2fs","xfs"]