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/p/[slug]/page.tsx

@@ -5,7 +5,7 @@ import { Megaphone } from "lucide-react";
 import { fetchSitePageBySlug, fetchOverview } from "@/lib/api";
 import { authCookieHeader } from "@/lib/cookies";
 import { getMeCached, getPublicSettingsCached } from "@/lib/serverData";
-import { isAdminOrAbove } from "@/lib/roles";
+import { hasPerm, PERMS } from "@/lib/roles";
 import { extractToc, estimateReadingMinutes, markdownHeadingToc } from "@/lib/toc";
 import MarkdownBody from "@/components/MarkdownBody";
 import PostToc from "@/components/PostToc";
@@ -58,7 +58,7 @@ export default async function SitePagePublic({ params }: PageProps) {
   const p = data.page;
   const sidebarPages = overview?.sidebar_pages ?? [];
   const announcements = overview?.announcements ?? [];
-  const canManagePages = !!me.user && isAdminOrAbove(me.user.role);
+  const canManagePages = !!me.user && hasPerm(me.user, PERMS.PAGES);
   const siteLead = settings.site_description?.trim() || undefined;
   const urlStyle = settings.url_style;
   const toc = extractToc(p.content);