Establish Community Health Files

[engichang1467]

Add Contributing Guidelines, Code of Conduct, and Standardize License

To prepare this repository for open-source contributions, we need to add standard community health files.

Tasks

• Create a CONTRIBUTING.md file in the root directory.
  • Include instructions on how to set up the environment using make setup-env and uv.
  • Explain how to run the existing smoke tests in tests/.
• Create a CODE_OF_CONDUCT.md (using the standard Contributor Covenant template).