Documentation changes

This PR bundles a few small updates

• Add breadcrumbs to the navigation page to improve discoverbaility
• Update the intro page for our API docs

Closes https://linear.app/mintlify/issue/DOC-6/improve-the-api-reference-introduction-page

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