Add development guidelines in CLAUDE.md

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CLAUDE.md

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+# Development Guidelines
+
+## Python Environment
+- Always use `python3` directly, never `python`
+- Run `black` code formatter after creating or modifying Python files
+
+## Git Workflow
+- Avoid committing unrelated untracked files (e.g., `node_modules/`, build artifacts)
+- Only commit relevant project files