feat: 代码片段功能与 Markdown 内嵌片段渲染、文档截图等

frontend/app/admin/settings/HeaderNavPanel.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { ArrowDown, ArrowUp, BookOpen, ExternalLink, Home, Plus, Trash2, Trophy } from "lucide-react";
+import { ArrowDown, ArrowUp, BookOpen, CodeXml, ExternalLink, Home, Plus, Trash2, Trophy } from "lucide-react";
 import { useEffect, useState } from "react";
 import { AdminSettingsActions, AdminSettingsGroup, AdminSwitch } from "@/components/admin";
 import { apiUpdateSiteSettings, type PublicSettings } from "@/lib/api";
@@ -19,6 +19,7 @@ const BUILTIN_ICONS: Record<HeaderNavBuiltinKey, React.ReactNode> = {
   home: <Home size={14} />,
   leaderboard: <Trophy size={14} />,
   library: <BookOpen size={14} />,
+  snippets: <CodeXml size={14} />,
 };
 
 /** 内置项目标页说明（实际地址随伪静态风格变化，不允许改地址） */
@@ -26,6 +27,7 @@ const BUILTIN_HINTS: Record<HeaderNavBuiltinKey, string> = {
   home: "站点首页 /",
   leaderboard: "排行榜页（地址随伪静态风格变化）",
   library: "书库页（地址随伪静态风格变化）",
+  snippets: "片段广场页（地址随伪静态风格变化）",
 };
 
 type BuiltinSwitches = Record<HeaderNavBuiltinKey, boolean>;
@@ -42,6 +44,7 @@ function switchesOf(items: HeaderNavItem[]): BuiltinSwitches {
     home: present.has("home"),
     leaderboard: present.has("leaderboard"),
     library: present.has("library"),
+    snippets: present.has("snippets"),
   };
 }