The previous commit sourced `ventoy/ventoy.cpio` from
`reference/Ventoy/INSTALL/ventoy/`, but `reference/` is in
.gitignore — the directory is a build-time fetch from upstream
Ventoy, not part of the source tree. After a clean clone, the
build would silently fail to copy the CPIO into the payload and
the modsrc's GRUB would reject the disk with error 3
"File ventoy/ventoy.cpio open failed in VTOYEFI partition".
Move the file to `vendor/ventoy-runtime/ventoy.cpio` (tracked) and
update package_release.sh to read from there. Source is upstream
Ventoy 1.0.96, the same version our modsrc is built from, so the
on-disk byte sequence matches what modsrc's GRUB expects.
