OpenRouter's /responses endpoint rejects store:true via Zod validation.
This is an endpoint-level limitation, not model-specific. The fix
conditionally omits the store parameter for OpenRouter while maintaining
it for direct OpenAI and Azure OpenAI providers.
- Add provider type check in _generate_with_responses_endpoint
- Include debug logging when store parameter is omitted
- Add regression tests for both OpenRouter and OpenAI behavior
Fixes#348