fix(homepage): align shell with zibll and restore post stream

Move header-slider outside main, render fluid zones once, default the
latest stream to plain posts by date, and cut dual-render/perf waste so
published posts and hero/banner structure match the zibll contract.

assets/css/frontend/header-components/base.css

@@ -195,6 +195,7 @@
 /* ============================================================
  * Container — 三层叠加的父容器
  * ============================================================ */
+.header-slider-container,
 .header-components-container {
     position: relative;
     isolation: isolate; /* 创建独立堆叠上下文，内部 z-index 不外泄 */