- Add github-copilot as LLM provider flavor in schema
- Implement GitHub Copilot API integration using OpenAI-compatible endpoint
- Add OAuth Device Flow implementation (RFC 8628) for GitHub authentication
- Configure GitHub OAuth endpoints and client ID
- Add comprehensive documentation for GitHub Copilot integration
This allows users to authenticate with GitHub and use GitHub Copilot models
(GPT-4o, GPT-4, etc.) directly in Rowboat using device code flow authentication.