Server-Timing：后端性能指标透出与前端度量协作

概述`Server-Timing` 响应头允许后端将关键阶段的耗时与描述透出，前端可通过 `PerformanceNavigationTiming.serverTiming` 获取并上报，实现端到端性能观测与优化。用法/示例HTTP/1.1 200 OK Server-Timing: db;dur=34;desc="query" , app;dur=12;desc="render" const nav = performance.getEntriesByType('navigation')[0] for (const st of nav.serverTiming) { console.log(st.name, st.duration, st.description) } 工程建议统一服务端指标命名与单位，避免歧义；仅暴露必要阶段并控制头大小。与 RUM 系统打通，结合前端指标（LCP/INP/CLS）进行关联分析。对跨源代理与缓存链路进行校验，确保头信息不被丢弃或篡改。参考与验证MDN：Server-Timing — https://developer.mozilla.org/docs/Web/HTTP/Headers/Server-Timingweb.dev：Server Timing — https://web.dev/articles/server-timingW3C：Resource Timing — https://www.w3.org/TR/resource-timing-2/