Service level: BAN_MEMBERS refusal (Forbidden even for nonexistent targets
— no id enumeration), equal-rank and owner-target hierarchy refusals,
authorized ban/unban round-trip, self-ban rejection. Admin API level:
equal-rank owner ban 403s, a lower-positioned ADMINISTRATOR cannot ban the
owner, downward bans still work. All existing NewAdminAPI/NewHandler test
callsites now inject a real ModerationService so the production
authorization runs in every PATCH-user test.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>