docs: add RepoCloud one-click deploy button

[cosark]

Adds a RepoCloud one-click deploy button to the README, placed in a new "☁️ One-Click Deploy" section immediately after the existing "Deploy it" section.

• New ## ☁️ One-Click Deploy section added between "Deploy it" and "Try it"
• Button links to https://repocloud.io/details/OpenBot/

[davidmckayv]

Thanks for the interest in OpenBot. We're going to pass on this one.

OpenBot is a template to fork and deploy on your own infrastructure, and it already documents its deploy paths (Docker/Compose, and the Helm chart for Kubernetes). We don't put third-party hosting-vendor deploy buttons in the README: it's a specific vendor placement rather than a template capability, and endorsing one hosting provider in the project's own docs isn't a direction we want to take. Anyone who wants to run OpenBot on a particular platform is free to do so from the fork.

Closing as out of scope. No reflection on the work, it's just not something the template should carry.