Re-downloads the file content from its original source_url, replaces the file on disk,
and re-runs the RAG ingestion pipeline — regenerating embeddings, summary, and metadata.
The existing Upload record is updated in-place (no new record is created).
Only works for files that were originally uploaded via URL (source_url must be set).
Collection membership is preserved through the re-ingestion process.
JWT token passed in x-access-token header
The file ID to re-ingest