admin repo list [--owner] [--visibility] [--limit] [--cursor] with size and last push; admin repo archive|unarchive|visibility|delete, admin-gated, skipping the policy check and writing an admin repo.<action> audit row each. Reads are unchanged: a private repo still 404s to an admin, and the test asserts it.
Archive, visibility, and delete bodies are extracted from the user-facing runners and shared. duDir moves to gitutil.DirSize.
Wiki: Admin page updated, pushed with the merge.
Closes #71