Add cleanup-renamed-repos.sh, which groups Gitea mirrors and gitea-mirror
rows by GitHub repo id, keeps the copy at the current name (renaming a
case-only mismatch in place), deletes the rest and re-imports.
cleanup-archived-repos.sh now deletes every mirror whose GitHub source 404s
when the source belongs to the gh user or an org it administers, keeps
third-party ones, and aborts on a GitHub rate limit.
