Fetch a user submitted file (image or audio) for a given Task Run

Fetch an individual Task Run file. This endpoint retrieves files associated with a task run, such as: - Input images or audio files submitted for processing - Output images, audio, PDFs, or CSV files generated by the task The file is served with appropriate content type headers for inline viewing or download based on the `inline` parameter. `file_name` is the `stored_filename` from the run's `files` array, not the name the caller uploaded. Each entry there also carries a ready-made `download_url` for this endpoint. The response carries the stored file's own content type — a `.txt` attachment comes back as `text/plain`, not as an opaque byte stream — and a `Content-Disposition` header naming the stored file.