Docs on manually triggering builds and previews

[ethanpalm]

Documentation changes

This PR documents how to manually build your docs site and how to manually create a preview.

I added an article on deployments so that there is room to grow that topic with future content and this isn't appropriate for the quickstart. Open to opinions on the placement of the deployment content though.

Closes https://linear.app/mintlify/issue/DOC-45/how-to-retrigger-a-build

---

For Reviewers

When reviewing documentation PRs, please consider:

✅ Technical accuracy

• Code examples work as written
• Commands and configurations are correct
• Links resolve to the right destinations
• Prerequisites and requirements are accurate

✅ Clarity and completeness

• Instructions are clear and easy to follow
• Steps are in logical order
• Nothing important is missing
• Examples help illustrate the concepts

✅ User experience

• A new user could follow these docs successfully
• Common gotchas or edge cases are addressed
• Error messages or troubleshooting guidance is helpful

[hahnbeelee]

left some comments but otherwise LGTM!