admin user create|disable|enable|delete, admin email verify, admin invite, and admin stats join the registry, SSH-only and admin-gated. gitbayd admin becomes wrappers that run the registry command as the host (no actor, source: host in the audit row). --key <path> on the host feeds the file to stdin, which is --key - over SSH.
Output contracts the existing e2e tests assert on are unchanged. Left host-local: backup, gc, and the backfills.
Wiki: Admin page updated, pushed with the merge.
Closes #72