Changes
PR #1676 by ksylvan: Refactor authentication to support GITHUB_TOKEN and GH_TOKEN
- Refactor: centralize GitHub token retrieval logic into utility function
- Support both GITHUB_TOKEN and GH_TOKEN environment variables with fallback handling
- Add new util/token.go file for centralized token handling across the application
- Update walker.go and main.go to use the new centralized token utility function
- Feat: add 'gpt-5' to raw-mode models in OpenAI client to bypass structured chat message formatting