Fetch a URL and extract structured metadata from its HTML: title, description, canonical URL, language, favicon URL, RSS/Atom feed links, Open Graph tags (og:title, og:image, og:type, og:description, og:url), Twitter Card tags, and other meta tags (author, keywords, robots). Use this to get Open Graph data, preview cards, or site information without parsing HTML yourself. Send {"url": "https://..."}. Remote fetch timeout: 5s, max download size: 2 MB.