feat: 代码片段功能与 Markdown 内嵌片段渲染、文档截图等

frontend/components/admin/AdminShell.tsx

@@ -31,6 +31,7 @@ import {
   Layers,
   Images,
   Link2,
+  CodeXml,
 } from "lucide-react";
 import type { User } from "@/lib/api";
 import { apiAdminPendingCounts, apiLogout } from "@/lib/api";
@@ -118,6 +119,12 @@ const NAV_GROUPS: NavGroup[] = [
         icon: BookOpen,
         visible: (u) => hasPerm(u, PERMS.LIBRARY),
       },
+      {
+        href: "/admin/snippets",
+        label: "片段管理",
+        icon: CodeXml,
+        visible: (u) => isStaff(u.role),
+      },
       {
         href: "/admin/friend-links",
         label: "友情链接",