Delete a knowledge gap for good

Delete the gap and everything it holds (question text, context, requester, answers, transition history), plus its idempotency key, so a new identical question records a fresh gap. Unlike the dismissed transition, nothing stays. Who may delete which gap is the integrator's policy; unanswered_only=true lets it delete only while nobody has answered, checked in the same write (409 otherwise). Deleting a POT deletes its gaps; deactivating a workspace deletes all of its gaps.