Integration of Amazon Neptune Analytics (GraphRAG) in Brchat's Knowledge Bases Vector Store

## Describe the solution you'd like

Please release a version of Brchat in which Amazon Neptune Analytics (GraphRAG) can be used in the Knowledge Bases vector store.

## Why the solution needed

GraphRAG is a feature that enhances the accuracy of responses by utilizing information from multiple documents—a feature that is not available in the current version of Brchat.

## Additional context

For further details about GraphRAG, please refer to the following URLs. Note that the websites are in Japanese:
https://aws.amazon.com/jp/blogs/machine-learning/announcing-general-availability-of-amazon-bedrock-knowledge-bases-graphrag-with-amazon-neptune-analytics/
https://dev.classmethod.jp/articles/amazon-bedrock-knowledge-bases-graphrag-generally-available
https://dev.classmethod.jp/articles/knowledge-bases-graphrag/

## Implementation feasibility

Are you willing to collaborate with us to discuss the solution, decide on the approach, and assist with the implementation?

- No, I am unable to implement the feature, but I am open to discussing the solution.

Start by reviewing the three linked AWS and community references for Amazon Neptune Analytics GraphRAG, then inspect Brchat’s current Knowledge Bases vector store integration. Define the required integration points and release criteria before implementation; done means GraphRAG can be selected and used through the Knowledge Bases vector store.

Written by the indexing model from the issue text.