Get a presigned URL to download the content of a file by its unique identifier.

The response includes a short-lived URL that can be used to download the file directly from cloud storage without additional authentication. The URL is valid for 1 hour; call this endpoint again to mint a fresh URL when needed.

Download availability is based on upload completion and redaction/obfuscation readiness. It is separate from processing status: a file can still report pending or failed from the Get file by id endpoint while the original bytes are available for download.