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).]

[gmile]

Would it be possible to import API module into a custom python script to use it directly? If yes, could you please provide a simple example of how to do this?

(asking as barely a python expert, but interested in embedding graphrag as part of my custom python webserver)

[caster-Q]

Is there a demo that can run this index API?