Ingest a scouting video from a URL

Pulls a video from the provided presigned URL, stores it on the video bucket, creates the Video record and queues the MediaConvert transcode. Returns as soon as the transcode is queued, so job_status is null in this response — a scheduled sweep checks the transcode every minute and records PROGRESSING, then COMPLETE together with output_url and thumbnail_url, or ERROR or CANCELED, as MediaConvert reports them. A job_status of ERROR means MediaConvert refused the job; the Video id is still valid. The returned id can be attached to a scouting session via media_type=video on POST /api/vortex/user-event-uploads. Repeating the call for the same source object returns the existing record instead of ingesting it twice. Callers must allow at least 300 seconds for this request: the 120 second budget bounds the download alone, and the mediainfo probe, the copy of up to 500 MB to S3, the checksum and the insert all follow it unbounded. Callers must also generate the presigned URL at call time rather than in advance, and send a URL whose path ends with the file extension. Authenticated via X-API-Key.