Add CODE_OF_CONDUCT.md for Community Expectations

Description

Create a CODE_OF_CONDUCT.md file that defines expected behavior for contributors and maintainers. Review commonly used open-source Codes of Conduct for reference and adapt an appropriate version for this project.

The document should clearly describe:
- Expected respectful and professional behavior
- Unacceptable behavior
- Community responsibilities
- How conduct concerns should be reported
- How violations may be handled

Start by reviewing commonly used open-source Codes of Conduct, then create CODE_OF_CONDUCT.md for this project. Done means the document clearly covers respectful and unacceptable behavior, community responsibilities, reporting conduct concerns, and how violations may be handled.

Written by the indexing model from the issue text.