Add archiso package to live ISO for working initrd hook

mkinitcpio runs inside the airootfs chroot, so the archiso hook files
(/usr/lib/initcpio/hooks/archiso) must be installed there. Without this
the hook has no device-scanning logic and boots to an empty root mount.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/profile/packages.x86_64

@@ -48,6 +48,7 @@ brightnessctl
 playerctl
 
 # Arch tools
+archiso
 pacman-contrib
 polkit