Process a file into chunks ready for vector database storage.
Deprecated. This endpoint blocks until processing completes, which can hold a connection open for large files. Use POST /file-processors/jobs to submit the file asynchronously and poll GET /file-processors/jobs/{job_id} for the result. Supports direct upload via multipart form or processing files already uploaded to file storage via file_id. Exactly one of file or file_id must be provided.