[Feature Request] Implement Box integration

## Describe the solution you'd like

A seamless integration with [Box](https://www.box.com/home) that allows Claude within the bedrock-claude-chat application to securely access and interact with documents stored in a user’s Box account. This could include retrieving files, summarizing their contents, performing semantic search, and providing relevant responses based on the data available in Box.

## Why the solution needed

Many users store their documents and assets on Box. By integrating Box into bedrock-claude-chat, users can leverage Claude’s capabilities directly on their existing content, streamlining workflows and enhancing productivity without manually moving data to another storage solution. This also centralizes operations within the familiar Box environment, reducing friction and ensuring privacy and security compliance.

## Additional context

For the integration, it might be useful to have an OAuth-based authentication flow to ensure secure, scoped access to the user’s Box content. Additionally, leveraging Box’s APIs to retrieve file metadata, folder structures, and content previews could enrich the overall user experience. There may be opportunities to fine-tune Claude’s responses with context from Box-hosted documents, improving relevance and accuracy.

## Implementation feasibility

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

- [ ] Yes, I am able to implement the feature and create a pull request.
- [x] No, I am unable to implement the feature, but I am open to discussing the solution.

The issue names no files, tests, or entry points; start by locating the existing authentication and external-service integration paths in bedrock-chat. Clarify the Box OAuth scopes, document retrieval and search behavior, and acceptance criteria with maintainers before implementation.

Written by the indexing model from the issue text.