The get_available_models method in ModelProviderRegistry was only checking
for providers with SUPPORTED_MODELS attribute, which OpenRouter doesn't have.
This caused auto mode to fail with "No models available" error when only
OpenRouter API key was configured.
Added special handling for OpenRouter provider to check its _registry
for available models, ensuring auto mode works correctly with OpenRouter.
Added comprehensive tests to verify:
- Auto mode works with only OpenRouter configured
- Model restrictions are respected
- Graceful handling when no providers are available
- No crashes when OpenRouter lacks _registry attribute
Further fixes to tests
Pass O3 simulation test when keys are not set, along with a notice
Updated docs on testing, simulation tests / contributing
Support for OpenAI o4-mini and o4-mini-high
