Add `CLAUDE.md`

## Description

Add a `CLAUDE.md` file to this repository to provide repository-specific context and guidance when working with Claude Code.

The structure and expected content for `CLAUDE.md` are being defined in insightsengineering/nestdevs-tasks#121. The implementation should follow the agreed structure from that issue and adapt the content to this repository.

The `CLAUDE.md` should capture the relevant repository-specific information while following the common conventions agreed for the teal repositories.

## Acceptance criteria

* `CLAUDE.md` is added to the repository.
* The file follows the structure agreed in insightsengineering/nestdevs-tasks#121.
* Repository-specific guidance is included where relevant.

Start by reading insightsengineering/nestdevs-tasks#121 to find the agreed CLAUDE.md structure, then inspect this repository for relevant R-specific workflows and conventions. Add CLAUDE.md with repository-specific guidance that follows the shared structure; done means the file exists, uses the agreed format, and includes relevant project information.

Written by the indexing model from the issue text.