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/SiteDocPageNav.tsx

@@ -0,0 +1,57 @@
+import Link from "next/link";
+import { ChevronRight, Info } from "lucide-react";
+import type { SidebarPageItem } from "@/lib/api";
+import { pageGlyph } from "@/lib/pageGlyph";
+
+/** 侧栏单页兄弟目录（高亮当前 slug） */
+export default function SiteDocPageNav({
+  pages,
+  currentSlug,
+  title = "文档目录",
+}: {
+  pages: SidebarPageItem[];
+  currentSlug?: string;
+  title?: string;
+}) {
+  if (pages.length === 0) return null;
+
+  return (
+    <section className="j13-module j13-about flex min-h-0 flex-col" aria-label={title}>
+      <p className="j13-module-title mb-1 shrink-0">
+        <Info size={15} style={{ color: "var(--accent)" }} /> {title}
+      </p>
+      <ul className="j13-about-list j13-rail-scroll">
+        {pages.map((p) => {
+          const Icon = pageGlyph(p.slug);
+          const current = currentSlug === p.slug;
+          return (
+            <li key={p.id}>
+              <Link
+                href={`/p/${p.slug}`}
+                className="j13-about-item"
+                aria-current={current ? "page" : undefined}
+                style={
+                  current
+                    ? {
+                        background: "var(--accent-soft)",
+                        borderColor: "var(--nav-active-line)",
+                      }
+                    : undefined
+                }
+              >
+                <span className="j13-about-ico" aria-hidden="true">
+                  <Icon size={15} strokeWidth={2} />
+                </span>
+                <span className="j13-about-body">
+                  <span className="j13-about-name">{p.title}</span>
+                  {p.excerpt ? <span className="j13-about-excerpt">{p.excerpt}</span> : null}
+                </span>
+                <ChevronRight className="j13-about-chev" size={15} aria-hidden="true" />
+              </Link>
+            </li>
+          );
+        })}
+      </ul>
+    </section>
+  );
+}