Delete AI detection checks

Mark one or more AI detection checks as deleted so they no longer appear in the user's cabinet. Send the IDs as an array form field named id[].

id[] is required: a missing or empty id[] is rejected with 400 rather than reported as a successful deletion.

Every submitted ID must be a positive integer identifying a standalone AI check (type 3, not attached to a text check) that is not already deleted, and the authenticated user must be allowed to delete it. Deleting an already-deleted check answers 404 and leaves its original deletion date untouched. Nothing is deleted unless every submitted ID passes these checks. Deleted checks are no longer returned by GET /api/v1/chat-gpt/{id}/ or listed by GET /api/v1/documents/.