Insert new Documents

Insert 1–1000 documents. Supplied IDs are ignored unless the X-Corva-App header names an app in the client-ID allowlist. For those apps, regular collections preserve an optional _id, which must be a 24-character hexadecimal MongoDB ObjectId string; missing or null IDs are generated. Invalid IDs reject the whole request with HTTP 400 before insertion. Native time-series collections continue to ignore supplied IDs. Inserts never replace existing documents. Bulk write failures, including duplicate IDs, retain the HTTP 200 response with inserted_ids, failed_count, and messages.