The HTTP crawler strategy now checks Content-Type and Content-Disposition
headers to detect non-HTML file responses. When a file download is
detected, raw bytes are saved to disk and the path is returned via
downloaded_files. Text-based files (CSV, JSON, XML) also populate the
html field for backward compatibility. Binary files (PDF, images) set
html to empty string — content is only available via downloaded_files.
Adds downloads_path to HTTPCrawlerConfig (defaults to ~/.crawl4ai/downloads/).