Documentation changes

This PR is part of the project to convert to a task-based IA. It contains two parts of the project.

1. Convert the IA to be more task-based and add a Guides tab
2. Add an AI-native overview page to help people discover AI features since "AI optimization" is pushed farther down in the nav

Closes https://linear.app/mintlify/issue/DOC-162/create-ai-native-overview-page
Closes https://linear.app/mintlify/issue/DOC-161/convert-to-task-based-ia

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