POST /exploit-hazard/batch

Aggregate the local exploit hazard of a set of vulnerability instances (section 3.6 of the referenced paper): per-instance hazards, their sum as the aggregate daily hazard, and the Poisson probability of at least one exploitation event over the common horizon. Instances are the same objects the single endpoint accepts — or plain vulnerability-id strings — and optional shared 'parameters' (controls, KEV policy, Weibull shape) apply to every instance.