官方节假日发现与同步

从 gov.cn 官方节假日通知中发现、抓取并解析中国法定节假日与调休安排，生成结构化的节假日/补班日历数据。支持按年度频率控制探测、本地缓存复用，适用于构建中国工作日历、判断某日是否工作日、计算每周首个工作日等场景。 Discover and parse China's official holiday notices from gov.cn, normalize holiday and adjusted-workday rows, and apply frequency-controlled probing for any requested year. Use when Codex needs to build or explain a China business calendar, sync official holiday schedules into storage, determine the first workday of a week, or implement holiday-aware weekly sending logic.