Revoke Team Invitation

Withdraw a pending invite and free its seat.

404 for any code that is not THIS team's — other teams' codes and personal invites (team_id NULL) alike: confirming a foreign invitation id exists is the same disclosure the cross-user product and job routes refuse, and personal invites keep their existing admin-only revoke. 409 once accepted: the invitee is a member now, and unseating members is DELETE /api/teams/me/members/{id}, which has rules of its own.