Always route OpenAI-family providers through getOpenAIStreamFirstEventTimeoutMs so PI_OPENAI_STREAM_FIRST_EVENT_TIMEOUT_MS wins even when callers pass per-call streamIdleTimeoutMs. The OpenAI helper now floors the first-event budget at the caller-resolved idle (which already encompasses per-call streamIdleTimeoutMs or PI_OPENAI_STREAM_IDLE_TIMEOUT_MS upstream), and explicit env disables ("0") on either knob continue to drop the watchdog.
Fixes#1603