x-mint migrate script

[ethanpalm]

Documentation changes

This PR documents how to use the CLI migration tool to convert MDX endpoint pages to autogenerated pages.

Closes https://linear.app/mintlify/issue/DOC-140/cli-script-for-migrating-mdx-endpoint-pages

---

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

[mycho2003]

This looks great; just a few small things I wanted to tweak from my PR description before showing it to the world.

In particular, I think "referencing OpenAPI endpoints" might be a bit vague; it's possible to talk about them in text without generating a page. Maybe semantic, but just want to be safe.

I also think the migration of x-mcp isn't really the focus here, and doesn't need to be highlighted in this section.

[mycho2003]

Looks good once comments are resolved!