Coverage was 83.83% (below 85% threshold). Added mockito-based HTTP mock
tests for all OAuth device flow functions, list/create repo, get user,
and send_chat. Coverage now at 90.26%.
- github.rs: 55.99% → 94.85% (added mock tests for all HTTP functions)
- ai_chat.rs: 63.27% → 95.70% (added mock tests for send_chat paths)
- Added mockito = "1" as dev-dependency
- Refactored HTTP functions to accept configurable base URLs for testability