feat: add CLAUDE.md to share project guidelines with claude code

[thoo]

Summary

• Add CLAUDE.md that directs Claude Code to read AGENTS.md for all project guidelines
• Enables AI tools to automatically follow project conventions when creating PRs

Changes

• Created CLAUDE.md with simple reference to AGENTS.md
• Ensures consistent code style, import patterns, and testing practices in AI-generated contributions

Closes #2027

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[hangfei]

Thanks @thoo . Do you know if Claude can follow that file or we need some links?

[thoo]

It does. I have been using the similar setup in openai-agent-sdk here with claude code.