Index API

[dworthen]

Description

This PR pulls out the core library logic from the CLI layer into a dedicated API layer, useful for programmatic use cases. The CLI now calls out to the API layer.

Checklist

• [x] I have tested these changes locally.
• [x] I have reviewed the code changes.
• [ ] I have updated the documentation (if necessary).
• [ ] I have added appropriate unit tests (if applicable).

Additional Notes

[Add any additional notes or context that may be helpful for the reviewer(s).]