AsyncOpenAI falls back to OPENAI_API_KEY when api_key is unset, so
ChatOrcaRouter(model=...) with no key authenticated its requests to
api.orcarouter.ai with the user's OpenAI credentials. The shipped example
hit this path whenever ORCAROUTER_API_KEY was unset, and .env.example
documented a variable that nothing read.
Resolve api_key from the constructor then ORCAROUTER_API_KEY, and raise
ModelProviderError(401) when neither is set, matching ChatMistral.
Saurav Panda
be76e6ccee