Add basic CLAUDE.md file

Author: tnull

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Development Rules
+
+- Always ensure tests pass before committing.
+- Run `cargo fmt --all` after every code change
+- Never add new dependencies unless explicitly requested
+- Please always disclose the use of any AI tools in commit messages and PR descriptions
+- When adding new `.rs` files, please ensure to always add the licensing header as found in all other files.