feat: 公文三栏单页布局，并修复时间线目录跳转与样式

公告/单页对齐帖子详情三栏壳；时间线按日锚点可跳转，条目改为日志行并用暖金日期区分 feat 色。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/components/site-doc/index.ts

@@ -0,0 +1,8 @@
+export { default as SiteDocShell } from "./SiteDocShell";
+export { default as SiteDocIdentity } from "./SiteDocIdentity";
+export { default as SiteDocPageNav } from "./SiteDocPageNav";
+export { default as SiteDocAnnoNav } from "./SiteDocAnnoNav";
+export { default as SiteDocMasthead } from "./SiteDocMasthead";
+export { default as SiteDocBreadcrumb } from "./SiteDocBreadcrumb";
+export type { Crumb } from "./SiteDocBreadcrumb";
+export type { SiteDocIdentityKind } from "./SiteDocIdentity";