docs: add CLAUDE.md for AI-assisted curation context

Provides repository overview and guidelines for AI tools:
- Repository architecture and structure
- Reference to CONTRIBUTING.md for PR review criteria
- Key curation considerations

This document enables AI assistants to understand the project context and apply consistent review standards.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>