A merged aarch64 tree without a PR build artifact (expired after 7 days,
or a dispatch) was rebuilt on the x86 droplet under QEMU: omarchy-mac-boot
took ~167 of the 240 minutes. A new job builds it on ubuntu-24.04-arm the
way build-pr.yml does and uploads it under the same label, so the publish
job signs and uploads it on the droplet like a PR artifact. The plan logs
reuse or rebuild for every package; x86_64, signing and the publish
concurrency are unchanged.