docs: add CLAUDE.md and deployment architecture documentation (#528)

[dengwx2026]

Summary

• Add CLAUDE.md with project overview, architecture, code conventions, testing guide, and git workflow
• Add docs/dev/deployment/README.md with Mermaid architecture diagrams, Docker usage analysis, and proposals for need_docker test marker and early Docker validation in SandboxManager

Test plan

• Verify Mermaid diagrams render correctly on GitHub
• Review CLAUDE.md for accuracy against current codebase

fixes #528

🤖 Generated with Claude Code

[CLAassistant]

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