feat: 站点单页、时间线导入与行级 BBCode 短代码

首页右栏接入单页入口与公告置顶/全部页；Markdown 编辑器支持可视化时间线与 Git 导入；隐藏块改为 [hide]/[timeline] 命名闭合，并修复单页/公告 GORM 更新只改 updated_at 的问题。

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

frontend/app/p/[slug]/page.tsx

@@ -0,0 +1,84 @@
+import type { Metadata } from "next";
+import Link from "next/link";
+import { notFound } from "next/navigation";
+import { ChevronRight } from "lucide-react";
+import { fetchSitePageBySlug } from "@/lib/api";
+import { formatDate } from "@/lib/format";
+import MarkdownBody from "@/components/MarkdownBody";
+
+interface PageProps {
+  params: Promise<{ slug: string }>;
+}
+
+export async function generateMetadata({ params }: PageProps): Promise<Metadata> {
+  const { slug } = await params;
+  const data = await fetchSitePageBySlug(slug).catch(() => null);
+  if (!data) return { title: "页面不存在" };
+  const p = data.page;
+  return {
+    title: p.title,
+    description: p.excerpt || p.title,
+    openGraph: {
+      title: p.title,
+      description: p.excerpt || p.title,
+      type: "article",
+      publishedTime: p.created_at,
+    },
+  };
+}
+
+export default async function SitePagePublic({ params }: PageProps) {
+  const { slug } = await params;
+  const data = await fetchSitePageBySlug(slug).catch(() => null);
+  if (!data) notFound();
+
+  const p = data.page;
+  const jsonLd = {
+    "@context": "https://schema.org",
+    "@type": "Article",
+    headline: p.title,
+    description: p.excerpt || undefined,
+    datePublished: p.created_at,
+    dateModified: p.updated_at,
+  };
+
+  return (
+    <div className="max-w-3xl mx-auto">
+      <script
+        type="application/ld+json"
+        dangerouslySetInnerHTML={{ __html: JSON.stringify(jsonLd) }}
+      />
+
+      <nav className="meta mb-5 flex items-center gap-1.5 text-[13px]">
+        <Link href="/" className="hover:text-[var(--accent)] transition-colors">
+          首页
+        </Link>
+        <ChevronRight size={13} />
+        <span className="truncate" style={{ color: "var(--accent)" }}>
+          {p.title}
+        </span>
+      </nav>
+
+      <article className="panel p-6 sm:p-8">
+        <time className="meta text-[12px] tabular-nums" dateTime={p.updated_at || p.created_at}>
+          {formatDate(p.updated_at || p.created_at)}
+        </time>
+        <h1
+          className="mt-2 text-[24px] sm:text-[28px] font-extrabold leading-snug tracking-tight"
+          style={{ color: "var(--ink)" }}
+        >
+          {p.title}
+        </h1>
+        {p.excerpt ? (
+          <p className="mt-3 text-[14.5px] leading-relaxed" style={{ color: "var(--ink-2)" }}>
+            {p.excerpt}
+          </p>
+        ) : null}
+
+        <div className="mt-5 pt-5" style={{ borderTop: "1px solid var(--line)" }}>
+          <MarkdownBody content={p.content} />
+        </div>
+      </article>
+    </div>
+  );
+}