Design GitHub Copilot Integration

• Task 59: Design GitHub Copilot Integration

  • Created comprehensive design proposal for GitHub Copilot as third LLM provider
  • Designed CopilotClient following existing LLMClient interface patterns
  • Planned GitHub authentication and session management architecture
  • Specified real-time status update mechanisms using polling and streaming
  • Documented complete implementation plan with file-by-file changes
  • Created COPILOT_PROPOSAL.md with technical specifications and rollout strategy (2025-01-27)