Gitea stays the source of truth and push-mirrors every commit and tag to
GitHub. With the organization variable BUILD_ON=github, GitHub's ci.yml runs
the tests, the Docker build check and, on tags, the multi-arch image publish
on native amd64 and arm64 runners, pushing to the Gitea registry and posting a
commit status back. Gitea's build jobs skip, and a new `github` job waits for
that status so the Gitea run still passes or fails with the real result.
With BUILD_ON unset nothing changes: GitHub's jobs skip and Gitea builds as
before, which is also the fallback if GitHub is unavailable.
The GitHub-era release, publish and cleanup workflows are removed -- the
weekly release is cut on Gitea and images no longer go to GHCR -- and so is
dependabot.yml, whose pull request branches every mirror sync would delete.
jcoffey-dev