- Add 'github-user' fallback in WaitForAuthorization when FetchUserInfo
returns empty Login (fixes malformed 'github-copilot-.json' filenames)
- Standardize Web API file name to 'github-copilot-<user>.json' to match
CLI path convention (was 'github-<user>.json')
Addresses Gemini Code Assist review comments on PR #291.