Render a zone with the name in the body

Web-friendly zone rendering at POST /zones. Intended for direct use from a browser page or web SDK embed — accepts form-encoded, plain-text, and multipart bodies in addition to JSON, and handles cookie-based identity automatically. Renders the zone identified by event_name in the request body, applies any other body fields as targeting data passed to the creative, and returns the rendered creative content (HTML, JavaScript, JSON, or plain text). If event_name is omitted, returns an empty 200 with Extole-Log: target zone=unknown; the access token is still allocated and written as a cookie. For backend zone rendering use POST /api/v6/zones instead.