fix(core): reject ignored explicit-client options for OpenAIProvider

[sylvesterkaczmarek]

Summary

• reject organization and project when openai_client is supplied
• align them with existing rejection of api_key, base_url, and websocket_base_url
• prevent documented client-construction options from being silently ignored

When an explicit AsyncOpenAI client is supplied, client-construction options cannot affect that client. Failing fast avoids configuration that appears to be applied but is actually discarded.

Test plan

• added focused regression coverage in tests/test_openai_provider_client_options.py
• GitHub Actions

Issue number

N/A