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/links/LinksBoard.tsx

@@ -11,6 +11,7 @@ import {
   type FriendLinkStatus,
 } from "@/lib/api";
 import LinksClient from "./LinksClient";
+import { densitySrcSet, isOwnImage, pickVariantWidth, variantURL } from "@/lib/responsiveImage";
 
 interface Props {
   links: FriendLink[];
@@ -240,9 +241,11 @@ export default function LinksBoard({
                         {/* 头部：LOGO + 名称 + 状态 */}
                         <div className="flex items-center gap-3">
                           {edit.logo_url ? (
+                            // 40px 位：本站图走 48/96 变体；外链保持原样
                             // eslint-disable-next-line @next/next/no-img-element
                             <img
-                              src={edit.logo_url}
+                              src={isOwnImage(edit.logo_url) ? variantURL(edit.logo_url, pickVariantWidth(40)) : edit.logo_url}
+                              srcSet={isOwnImage(edit.logo_url) ? densitySrcSet(edit.logo_url, 40) : undefined}
                               alt=""
                               width={40}
                               height={40}
@@ -475,9 +478,11 @@ export default function LinksBoard({
               }}
             >
               {l.logo_url ? (
+                // 48px 位：本站图走 48/96 变体；外链保持原样
                 // eslint-disable-next-line @next/next/no-img-element
                 <img
-                  src={l.logo_url}
+                  src={isOwnImage(l.logo_url) ? variantURL(l.logo_url, pickVariantWidth(48)) : l.logo_url}
+                  srcSet={isOwnImage(l.logo_url) ? densitySrcSet(l.logo_url, 48) : undefined}
                   alt=""
                   loading="lazy"
                   width={48}

frontend/app/links/LinksClient.tsx

@@ -4,6 +4,7 @@ import { useRef, useState } from "react";
 import Link from "next/link";
 import { Loader2, Upload } from "lucide-react";
 import { apiApplyFriendLink, apiUploadPostImage } from "@/lib/api";
+import { densitySrcSet, isOwnImage, pickVariantWidth, variantURL } from "@/lib/responsiveImage";
 
 interface Props {
   isLoggedIn: boolean;
@@ -155,9 +156,11 @@ export default function LinksClient({ isLoggedIn, canManage, onClose }: Props) {
             aria-hidden
           >
             {form.logo_url ? (
+              // 64px 预览位：本站图走 96/160 变体；外链地址保持原样
               // eslint-disable-next-line @next/next/no-img-element
               <img
-                src={form.logo_url}
+                src={isOwnImage(form.logo_url) ? variantURL(form.logo_url, pickVariantWidth(64)) : form.logo_url}
+                srcSet={isOwnImage(form.logo_url) ? densitySrcSet(form.logo_url, 64) : undefined}
                 alt=""
                 className="h-full w-full object-contain"
                 onError={(e) => {

frontend/app/links/page.tsx

@@ -4,7 +4,7 @@ import { fetchFriendLinks, fetchSiteState, type FriendLink } from "@/lib/api";
 import { authCookieHeader } from "@/lib/cookies";
 import { brandAliasPath } from "@/lib/brand";
 import { getMeCached, getPublicSettingsCached } from "@/lib/serverData";
-import { isAdminOrAbove } from "@/lib/roles";
+import { hasPerm, PERMS } from "@/lib/roles";
 import { requestCanonical } from "@/lib/canonicalMeta";
 import { resolveSiteOrigin } from "@/lib/siteUrl";
 import LinksBoard from "./LinksBoard";
@@ -34,7 +34,7 @@ export default async function FriendLinksPage() {
     getMeCached(cookie || undefined),
   ]);
   const isLoggedIn = !!me.user;
-  const canManage = !!me.user && isAdminOrAbove(me.user.role);
+  const canManage = !!me.user && hasPerm(me.user, PERMS.ANNOUNCEMENTS);
   // 站点 LOGO 用固定对外地址（换图不变链，对方收藏的地址永不失效），补全为绝对地址供申请人直接复制
   const siteBase = siteState.site_url?.trim() || resolveSiteOrigin() || "";
   const logoAlias = settings.logo_light_url