Add Deploy to Railyard button

[almokhtarbr]

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/

Just the one badge line — feel free to close if you would rather not carry it.

[github-actions]

👋 Thanks for the contribution! LibreChat merges all changes into dev first — main only moves at release time — so this pull request's base branch was switched from main to dev automatically.

Nothing is needed from you; your commits, reviews and discussion are unchanged. If the diff now shows files you did not touch, rebase onto dev:

git remote add upstream https://github.com/LibreChat-AI/LibreChat.git
git fetch upstream dev
git rebase upstream/dev
git push --force-with-lease

Maintainers: apply the target: main label and restore the base branch if this one genuinely belongs on main.

[berry-13]

BerriAI/litellm#44630 (review)