Giving a Telegram bot's photos a real social preview card

Kitty Space started as a Telegram bot. People send photos of street cats, the bot saves them, and it sends a link back. The next thing everyone wanted was to share that cat on Twitter or in a chat. Paste the link, though, and no preview showed up: a bare URL, or at best a card with no image. Here is what we found, and the small server built around it.