Fetch a Box shared-link video when download is disabled

When Box box_download_shared_file returns 403 (download disabled on the share), the file is still retrievable via the preview representations pipeline. From the page context: read window.Box.config.requestToken, POST it as header X-Request-Token to /app-api/enduserapp/elements/tokens with body {fileIDs:["file_<id>"]} to get a downscoped read token. Then GET https://api.box.com/2.0/files/<id>?fields=representations with headers Authorization: Bearer <token> and BoxApi: shared_link=<share-url>. The mp4 representation content URL on public.boxcloud.com supports Range requests and is a smaller preview transcode, ideal for piping to ffmpeg + whisper for transcription.