Get one answer request with its questions and saved answers

The read behind the responder's answer page and the reviewer's per-company panel: one answer request merged with the questionnaire it answers, plus every question and the responder's saved answer. Note which half of the merge wins — id, status and dueDate are the questionnaire's, while the request's own are questionnaireRequestId and requestStatus. Attachments referenced by a question or an answer carry a 24-hour signed URL. Readable by the requesting company, the company being asked, and the company answering on its behalf; anyone else gets 404 rather than 403, so the endpoint never confirms a request they cannot read exists. An archived questionnaire answers 403.