archiso keeps vmlinuz/initramfs in the ISO boot dir, not the squashfs, so
unpackfs lays down an empty /boot. The chroot's mkinitcpio/grub-mkconfig had
nothing to work with and the ESP ended up empty (firmware found no bootloader).
- shellprocess@kernel (dontChroot) copies the live kernel into the target
/boot before the bootloader step
- post-install.sh now runs grub-install itself, including a --removable pass
so firmware with no NVRAM entry still boots via EFI/BOOT/BOOTX64.EFI
