feat: 书库导入导出/图片变体/书籍搜索/小组件运行时等

新增：
- 书库导入导出（library_import/library_export）及测试
- 图片变体生成（image_variants）与响应式图片（responsiveImage）
- 书籍搜索（bookSearch）+ BookSearch/LibrarySearchGrid 组件
- 小组件运行时（widgetRuntime）与静态检查（widgetLint）
- 上传缓存中间件（upload_cache）与字体 CSS 提取脚本

其它：
- 后端 handlers/services 全量调整
- 前端页面、组件、库函数与配置更新

frontend/components/admin/AdminShell.tsx

@@ -37,10 +37,12 @@ import { apiAdminPendingCounts, apiLogout } from "@/lib/api";
 import {
   canModerateAny,
   canAccessAdminMessages,
+  hasPerm,
   isAdminOrAbove,
   isOwner,
   isStaff,
   isSuperOrOwner,
+  PERMS,
   type RoleUserLike,
 } from "@/lib/roles";
 import { realtime, RT_MODERATION_CHANGED } from "@/lib/realtime";
@@ -102,19 +104,19 @@ const NAV_GROUPS: NavGroup[] = [
         href: "/admin/announcements",
         label: "公告管理",
         icon: Megaphone,
-        visible: (u) => isAdminOrAbove(u.role),
+        visible: (u) => hasPerm(u, PERMS.ANNOUNCEMENTS),
       },
       {
         href: "/admin/pages",
         label: "单页管理",
         icon: FileText,
-        visible: (u) => isAdminOrAbove(u.role),
+        visible: (u) => hasPerm(u, PERMS.PAGES),
       },
       {
         href: "/admin/library",
         label: "书库管理",
         icon: BookOpen,
-        visible: (u) => isAdminOrAbove(u.role),
+        visible: (u) => hasPerm(u, PERMS.LIBRARY),
       },
       {
         href: "/admin/friend-links",
@@ -155,7 +157,7 @@ const NAV_GROUPS: NavGroup[] = [
         href: "/admin/ads",
         label: "推广与赞助",
         icon: CircleDollarSign,
-        visible: (u) => isAdminOrAbove(u.role),
+        visible: (u) => hasPerm(u, PERMS.ADS),
       },
     ],
   },