Add RepoCloud one-click deploy button to README

[cosark]

Summary

Adds a "Deploy" section to the README with a one-click deploy button linking to RepoCloud, where OpenUI is available as a managed deployment.

Changes

• Added a new ## Deploy section between Live Demo and Running Locally
• Uses the same markdown image link format as the existing Gitpod button (no explicit height, SVG renders at natural size)

Why

RepoCloud offers managed hosting for open-source applications. This gives users an easy one-click option to deploy their own OpenUI instance without configuring Docker, API keys, or local environments.

Notes

• Button format matches the existing Gitpod deploy button convention in this README (SVG image, no height attribute)
• Placement follows the natural flow: Live Demo → Deploy your own → Running Locally