Checks a site's robots.txt and XML sitemap offline the way Google reads them. Picks the crawler's group, resolves longest-match Allow and Disallow with wildcards, and tests the URLs that must be crawlable or blocked. Flags whole-site blocks, sitemap URLs that robots.txt blocks, blocked CSS and JS, unsupported noindex and crawl-delay lines, off-site, duplicate or invalid sitemap entries. Includes a stdlib Python checker with --self-test.
