Backup verified: 80 commits, main @ 0d5c107, 208K, in scratchpad. Note the mirror also pulled refs/pull/* (GitHub-generated, not pushable) — I'll exclude those on any re-push.
One correction to your mental model: there is an official path. GitHub Support will detach a repo from its fork network on request, preserving everything including the URL, issues, and PRs. Some accounts also now have a self-serve Settings → General → "Leave fork network" button — worth you glancing at that page before we do anything manual, since it's one click if it's there.
So there are three routes:
| Preserves | Speed | Risk | |
|---|---|---|---|
| Self-serve button (if present) | everything | instant | none |
| Support ticket | everything | days | none |
| DIY recreate | code + history only | ~5 min | low (backed up) |
The DIY route is the one you described, and it works. It loses the 3 open issues, the merged PR #5 record, wiki, and collaborator list — all of which I can partially reconstruct.