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/admin/announcements/[id]/edit/AnnouncementEditLoader.tsx

@@ -0,0 +1,54 @@
+"use client";
+
+import { useEffect, useState } from "react";
+import { Loader2 } from "lucide-react";
+import { apiAdminListAnnouncements, type Announcement } from "@/lib/api";
+import AnnouncementComposeClient from "../../AnnouncementComposeClient";
+
+/** 无详情 API：从管理列表按 id 拉取后进入编辑器 */
+export default function AnnouncementEditLoader({ id }: { id: number }) {
+  const [item, setItem] = useState<Announcement | null>(null);
+  const [error, setError] = useState("");
+  const [loading, setLoading] = useState(true);
+
+  useEffect(() => {
+    let alive = true;
+    setLoading(true);
+    apiAdminListAnnouncements()
+      .then((res) => {
+        if (!alive) return;
+        const found = res.announcements.find((a) => a.id === id) ?? null;
+        if (!found) {
+          setError("公告不存在或已删除");
+          setItem(null);
+        } else {
+          setItem(found);
+          setError("");
+        }
+      })
+      .catch((e) => {
+        if (!alive) return;
+        setError(e instanceof Error ? e.message : "加载失败");
+      })
+      .finally(() => {
+        if (alive) setLoading(false);
+      });
+    return () => {
+      alive = false;
+    };
+  }, [id]);
+
+  if (loading) {
+    return (
+      <div className="panel p-10 flex items-center justify-center gap-2 meta">
+        <Loader2 size={18} className="animate-spin" /> 加载公告…
+      </div>
+    );
+  }
+
+  if (error || !item) {
+    return <p className="alert-error">{error || "公告不存在"}</p>;
+  }
+
+  return <AnnouncementComposeClient mode="edit" initial={item} />;
+}

frontend/app/admin/announcements/[id]/edit/page.tsx

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+import type { Metadata } from "next";
+import { cookies } from "next/headers";
+import { authCookieHeader } from "@/lib/cookies";
+import { getMeCached } from "@/lib/serverData";
+import { isAdminOrAbove } from "@/lib/roles";
+import Forbidden from "../../../Forbidden";
+import AnnouncementEditLoader from "./AnnouncementEditLoader";
+
+export const metadata: Metadata = {
+  title: "编辑公告",
+};
+
+interface PageProps {
+  params: Promise<{ id: string }>;
+}
+
+export default async function AdminAnnouncementEditPage({ params }: PageProps) {
+  const { id } = await params;
+  const cookie = authCookieHeader(await cookies());
+  const me = await getMeCached(cookie || undefined);
+  if (!me.user || !isAdminOrAbove(me.user.role)) {
+    return <Forbidden text="公告管理仅管理员及以上角色可操作。" />;
+  }
+
+  const numId = parseInt(id, 10);
+  if (!Number.isFinite(numId) || numId <= 0) {
+    return <Forbidden text="无效的公告 ID。" />;
+  }
+
+  return <AnnouncementEditLoader id={numId} />;
+}