混合搜索：需求和相关性契约
定义了一个混合检索契约，结合了词汇和语义候选，同时保留过滤器、授权、可解释的贡献信号以及可衡量的相关性行为。
Defines a reference job-board architecture with separate vacancy, employer, candidate, search, application, moderation, communication, and analytics boundaries plus the identities and events joining them.