Fetch a public web page and return just the main article as clean Markdown, with title, byline and excerpt. Menus, ads and footers are removed. Use when you need to read, summarise or quote a web page cheaply without parsing HTML yourself. Returns JSON {title, byline, siteName, excerpt, markdown}. Errors: 400 bad or private URL, 422 no readable article, 502 site returned an error.