rc.2 proved the grype gate was decorative — buildx pushed before the
scan ran, so a red run still shipped the image (and rc tags moved
:latest). Build amd64 locally, scan that, then run the multi-arch push
from the warm builder cache. :latest now only moves on non-rc tags.
mirror-release: poll until the Gitea asset count is stable across two
polls (GoReleaser uploads sequentially — assets>0 could mirror a partial
set) and stretch the timeout to 20 min since the release run can queue
behind the Docker job on the single runner.