Remove the title input and header image upload/generate section from
the thread builder editor. Title is now auto-derived from first tweet.
Add link preview cards that render inline in tweet content, similar to
Twitter's URL card unfurling. Server-side /api/link-preview endpoint
fetches OG metadata (title, description, image) with caching.
URLs in tweet text are rendered as clickable links.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>