Add OcspChainValidationEvent DTO, OcspStatus enum, and OcspEventBuilder helper with BuildPeerReject, BuildChainValidation, and ParseStatus methods. Register OcspChainValidationEvent in EventJsonContext source-gen context. Add OcspPeerReject and OcspChainValidation subject constants to EventSubjects. 10 new tests in OcspEventTests cover all DTOs, builder methods, status parsing, and JSON round-trip.