Fix unbootable installs: lay the kernel into the target and own GRUB

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

iso/profiledef.sh

@@ -19,4 +19,5 @@ file_permissions=(
     ["/etc/calamares/post-install.sh"]="0:0:755"
     ["/usr/local/bin/bos-live-setup"]="0:0:755"
     ["/usr/local/bin/bos-launch-calamares"]="0:0:755"
+    ["/usr/local/bin/bos-copy-kernel"]="0:0:755"
 )