Fix archiso bootmodes and add syslinux to package list

mkarchiso validation: bios.syslinux.mbr/eltorito and uefi-x64.* bootmodes
are deprecated -> use bios.syslinux + uefi.systemd-boot. syslinux must be
in the package list for the BIOS bootmode; add memtest86+/edk2-shell too.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

iso/packages.x86_64

@@ -11,6 +11,11 @@ efibootmgr
 btrfs-progs
 dosfstools
 mtools
+# Live-ISO boot (archiso bootmodes: bios.syslinux + uefi.systemd-boot)
+syslinux
+memtest86+
+memtest86+-efi
+edk2-shell
 
 # Snapshot infrastructure
 snapper

iso/profiledef.sh

@@ -8,12 +8,7 @@ iso_application="Bread Operating System"
 iso_version="$(date +%Y.%m.%d)"
 install_dir="arch"
 buildmodes=('iso')
-bootmodes=(
+bootmodes=('bios.syslinux' 'uefi.systemd-boot')
-    'bios.syslinux.mbr'
-    'bios.syslinux.eltorito'
-    'uefi-x64.systemd-boot.esp'
-    'uefi-x64.systemd-boot.eltorito'
-)
 arch="x86_64"
 pacman_conf="pacman.conf"
 airootfs_image_type="squashfs"