<https://github.com/Disfactory/Disfactory/pull/699|#699 Add Deploy to Railyard button>

Adds a one-click "Deploy to Railyard" button next to your existing deploy links, for people who want to run this on their own server (DigitalOcean, Hetzner, Vultr, or any VPS over SSH) instead of a managed platform. Docs: <https://railyard.run/docs/deploy-button/|https://railyard.run/docs/deploy-button/> Just the one badge line — feel free to close if you would rather not carry it.