Add CONTRIBUTING.md guide for new developers

🔍 Summary

No CONTRIBUTING.md file found. This is the first file new contributors look for when joining a project.

📋 What Needs to Be Done

• Create CONTRIBUTING.md at repository root with:
  • Development environment setup instructions
  • Code style guidelines and linting configuration
  • Git workflow (branch naming, commit message conventions)
  • Pull request template and checklist
  • How to run tests locally
  • How to report bugs
  • Code of Conduct reference

💡 Template

GitHub provides a starter template: https://docs.github.com/en/communities/setting-up-your-project-for-healthy-contributions/setting-guidelines-for-repository-contributors