Add --auth-choice minimax-api for direct MiniMax API usage at
https://api.minimax.io/anthropic using the anthropic-messages API.
Changes:
- Add applyMinimaxApiConfig() function with provider/model config
- Add minimax-api to AuthChoice type and CLI options
- Add handler and non-interactive support
- Fix duplicate minimax entry in envMap
- Update live test to use anthropic-messages API
- Add 11 unit tests covering all edge cases
- Document configuration in gateway docs
Test results:
- 11/11 unit tests pass
- 1/1 live API test passes (verified with real API key)
Co-Authored-By: Claude <noreply@anthropic.com>
