Delete Public Repo

Delete a public repo and everything derived from it, for everyone.

This is not the per-user unlink at DELETE /repos/{id}. It removes the shared repo row, so Postgres cascades away every user's library entry, every workspace membership, every team share, and every snapshot. People who did not ask for this lose the repo from their dashboard.

Which is why confirm has to spell out owner/name, why the affected counts are read before the cascade destroys them, and why the audit row is written before the purge rather than after.

Refuses while an index is in flight. Deleting mid-run cascades away the snapshots row while the Modal container is still uploading to its prefix, and anything it writes to R2 after that point is unreachable forever, since nothing sweeps R2 orphans.