Replaces the bespoke xorriso -as mkisofs invocation (and its EFI
partition dd extraction) with a single -boot_image any replay -map call
that preserves the source ISO's MBR, GPT, El Torito and archiso layout
flags byte-for-byte. The previous approach dropped --mbr-force-bootable,
-partition_offset 16, -iso_mbr_part_type 0x00 and -partition_cyl_align
off, which Omarchy 3.6's stricter mkarchiso layout requires — without
them the rebuilt ISO hung at the boot splash on Acer Insyde, Lenovo and
MSI firmware. Also recompute airootfs.sha512 in case a future archiso
ever enables verify=y on the kernel cmdline. Works for any Omarchy
version (3.4, 3.5, 3.6, future) without per-version tweaks.
