feat: 关于本站对齐站点公告，增加全部与管理入口

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

frontend/app/announcements/page.tsx

@@ -1,8 +1,11 @@
 import type { Metadata } from "next";
+import { cookies } from "next/headers";
 import Link from "next/link";
 import { Megaphone } from "lucide-react";
 import { fetchAnnouncementsPage, fetchOverview, type Announcement } from "@/lib/api";
-import { getPublicSettingsCached } from "@/lib/serverData";
+import { authCookieHeader } from "@/lib/cookies";
+import { getMeCached, getPublicSettingsCached } from "@/lib/serverData";
+import { isAdminOrAbove } from "@/lib/roles";
 import { formatDate } from "@/lib/format";
 import Pagination from "@/components/Pagination";
 import {
@@ -114,19 +117,24 @@ export default async function AnnouncementsListPage({ searchParams }: PageProps)
     error = e instanceof Error ? e.message : "加载公告失败";
   }
 
-  const [overview, settings] = await Promise.all([
+  const cookie = authCookieHeader(await cookies());
+  const [overview, settings, me] = await Promise.all([
     fetchOverview().catch(() => null),
     getPublicSettingsCached(),
+    getMeCached(cookie || undefined),
   ]);
   const sidebarPages = overview?.sidebar_pages ?? [];
   const siteLead = settings.site_description?.trim() || undefined;
+  const canManagePages = !!me.user && isAdminOrAbove(me.user.role);
 
   // 首页置顶条目作头图；其余走列表行（置顶已在头图时不再重复）
   const featured = page === 1 ? announcements.find((a) => a.pinned) : undefined;
   const rest = featured ? announcements.filter((a) => a.id !== featured.id) : announcements;
 
   const left = <SiteDocIdentity kind="announcements" lead={siteLead} />;
-  const right = <SiteDocPageNav pages={sidebarPages} title="关于本站" />;
+  const right = (
+    <SiteDocPageNav pages={sidebarPages} title="关于本站" canManage={canManagePages} />
+  );
 
   return (
     <SiteDocShell
@@ -140,7 +148,9 @@ export default async function AnnouncementsListPage({ searchParams }: PageProps)
           ]}
         />
       }
-      mobileExtras={<SiteDocPageNav pages={sidebarPages} title="关于本站" />}
+      mobileExtras={
+        <SiteDocPageNav pages={sidebarPages} title="关于本站" canManage={canManagePages} />
+      }
     >
       <header className="mb-5">
         <h1