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/app/page.tsx

@@ -18,7 +18,7 @@ import SidebarRenderer, { type SidebarBlockProps } from "@/components/sidebar/Si
 import { authCookieHeader } from "@/lib/cookies";
 import { getMeCached, getPublicSettingsCached } from "@/lib/serverData";
 import { siteDocumentTitle } from "@/lib/brand";
-import { isAdminOrAbove } from "@/lib/roles";
+import { hasPerm, PERMS } from "@/lib/roles";
 import Pagination from "@/components/Pagination";
 import PostRow from "@/components/PostRow";
 import FeedTabs from "@/components/home/FeedTabs";
@@ -127,8 +127,8 @@ export default async function HomePage({ searchParams }: HomePageProps) {
   const sidebar = sidebarData ?? { config: defaultSidebarConfig(), widgets: [] };
   const user = me.user;
   const boards = overview?.boards ?? [];
-  const canManageAnnouncements = !!user && isAdminOrAbove(user.role);
-  const canManagePages = canManageAnnouncements;
+  const canManageAnnouncements = !!user && hasPerm(user, PERMS.ANNOUNCEMENTS);
+  const canManagePages = !!user && hasPerm(user, PERMS.PAGES);
   const sidebarPages = overview?.sidebar_pages ?? [];
   const activeBoard = boards.find((b) => b.id === boardId) || boardSidebar?.board || null;
   const showBoardPanels = boardId > 0 && !isSearch;