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/library/page.tsx

@@ -1,106 +1,9 @@
 import type { Metadata } from "next";
-import type { CSSProperties } from "react";
-import Link from "next/link";
-import { BookOpen, FileDown } from "lucide-react";
 import { fetchLibraryList, type LibraryDocListItem } from "@/lib/api";
-import { coverHue } from "@/lib/coverColor";
 import { getPublicSettingsCached } from "@/lib/serverData";
 import { requestCanonical } from "@/lib/canonicalMeta";
-import { libraryPath, libraryDocPath } from "@/lib/urlStyle";
-
-function formatSize(n: number): string {
-  if (!Number.isFinite(n) || n <= 0) return "0 B";
-  if (n < 1024) return `${n} B`;
-  if (n < 1024 * 1024) return `${(n / 1024).toFixed(1)} KB`;
-  return `${(n / (1024 * 1024)).toFixed(1)} MB`;
-}
-
-/** 文字封面：无图时用完整书名 + 书名派生稳定色相洗底（lib/coverColor.ts） */
-function TextCover({ title }: { title: string }) {
-  const name = title.trim() || "书";
-  return (
-    <div
-      className="j13-text-cover w-full h-full flex items-center justify-center px-5 select-none"
-      style={{ "--cover-h": coverHue(name) } as CSSProperties}
-      aria-hidden
-    >
-      <span
-        className="text-[22px] font-extrabold leading-snug text-center line-clamp-3 break-all"
-      >
-        {name}
-      </span>
-    </div>
-  );
-}
-
-function ExtChip({ ext }: { ext: string }) {
-  return (
-    <span
-      className="text-[10.5px] font-semibold px-1.5 py-0.5 rounded-md uppercase tracking-wide"
-      style={{
-        color: "var(--accent)",
-        background: "var(--accent-soft)",
-        border: "1px solid color-mix(in srgb, var(--accent) 30%, transparent)",
-      }}
-    >
-      {ext}
-    </span>
-  );
-}
-
-function DocCard({
-  doc,
-  href,
-}: {
-  doc: LibraryDocListItem;
-  href: string;
-}) {
-  const exts = Array.from(new Set(doc.files.map((f) => f.ext))).slice(0, 4);
-  const totalSize = doc.files.reduce((acc, f) => acc + f.size, 0);
-  return (
-    <Link
-      href={href}
-      className="group flex flex-col overflow-hidden rounded-[20px] transition-transform hover:-translate-y-0.5"
-      style={{
-        background: "var(--panel)",
-        border: "1px solid var(--line)",
-      }}
-    >
-      <div className="h-36 overflow-hidden" style={{ borderBottom: "1px solid var(--line)" }}>
-        {doc.cover_url ? (
-          // eslint-disable-next-line @next/next/no-img-element
-          <img
-            src={doc.cover_url}
-            alt={doc.title}
-            className="w-full h-full object-cover transition-transform duration-300 group-hover:scale-[1.03]"
-            loading="lazy"
-            decoding="async"
-            draggable={false}
-          />
-        ) : (
-          <TextCover title={doc.title} />
-        )}
-      </div>
-      <div className="p-4 flex flex-col gap-2 flex-1">
-        <h2
-          className="text-[15px] font-bold leading-snug line-clamp-2"
-          style={{ color: "var(--ink)" }}
-        >
-          {doc.title}
-        </h2>
-        <div className="mt-auto flex flex-wrap items-center gap-1.5">
-          {exts.map((ext) => (
-            <ExtChip key={ext} ext={ext} />
-          ))}
-          <span className="meta text-[11px] ml-auto inline-flex items-center gap-1">
-            <FileDown size={11} />
-            {doc.file_count > 0 ? `${doc.file_count} 个文件 · ${formatSize(totalSize)}` : "暂无文件"}
-          </span>
-        </div>
-      </div>
-    </Link>
-  );
-}
+import { libraryPath } from "@/lib/urlStyle";
+import LibrarySearchGrid from "@/components/LibrarySearchGrid";
 
 export async function generateMetadata(): Promise<Metadata> {
   const settings = await getPublicSettingsCached();
@@ -113,7 +16,6 @@ export async function generateMetadata(): Promise<Metadata> {
 
 export default async function LibraryPage() {
   const settings = await getPublicSettingsCached();
-  const urlStyle = settings.url_style;
 
   // 接口失败降级为空态，不让页面 500
   let docs: LibraryDocListItem[] = [];
@@ -126,53 +28,52 @@ export default async function LibraryPage() {
 
   return (
     <div className="min-w-0">
-      {/* Hero：渐变洗底（与排行榜同语言） */}
+      {/* Hero：书香气——serif 大标题、两侧晕染、底部水纹线 */}
       <section
-        className="relative overflow-hidden rounded-[28px] px-6 py-8 sm:px-10 sm:py-10 text-center"
+        className="relative overflow-hidden px-6 py-12 sm:px-12 sm:py-16 text-center"
         style={{
           background:
-            "radial-gradient(120% 160% at 12% -10%, color-mix(in srgb, var(--accent) 16%, transparent), transparent 55%)," +
-            "radial-gradient(90% 140% at 90% -20%, color-mix(in srgb, var(--accent) 8%, transparent), transparent 50%)",
-          border: "1px solid var(--line)",
+            "radial-gradient(140% 180% at 50% -20%, color-mix(in srgb, var(--accent) 14%, transparent), transparent 60%)," +
+            "radial-gradient(80% 120% at 8% 0%, color-mix(in srgb, var(--accent) 6%, transparent), transparent 50%)," +
+            "radial-gradient(80% 120% at 92% 0%, color-mix(in srgb, var(--accent) 6%, transparent), transparent 50%)",
         }}
       >
         <div
           aria-hidden
-          className="absolute -top-16 -right-10 w-56 h-56 rounded-full pointer-events-none"
+          className="absolute left-1/2 top-1/2 -translate-x-1/2 -translate-y-1/2 w-[520px] h-[520px] rounded-full pointer-events-none"
           style={{
-            background: "color-mix(in srgb, var(--accent) 14%, transparent)",
-            filter: "blur(48px)",
+            background: "color-mix(in srgb, var(--accent) 10%, transparent)",
+            filter: "blur(72px)",
           }}
         />
         <div className="relative">
+          <p
+            className="text-[11px] sm:text-[12px] font-semibold tracking-[0.35em] uppercase mb-4"
+            style={{ color: "var(--accent)" }}
+          >
+            Library
+          </p>
           <h1
-            className="text-[26px] sm:text-[32px] leading-tight font-extrabold tracking-tight inline-flex items-center gap-2.5"
+            className="j13-library-title text-[32px] sm:text-[44px] leading-tight font-bold tracking-wide"
             style={{ color: "var(--ink)" }}
           >
-            <BookOpen size={26} style={{ color: "var(--accent)" }} />
             书库
           </h1>
-          <p className="meta mt-2 text-[13.5px]">书籍、文档与页面作品，在线阅读或下载</p>
+          <div
+            aria-hidden
+            className="mx-auto mt-5 h-px w-24 sm:w-32"
+            style={{
+              background:
+                "linear-gradient(90deg, transparent, color-mix(in srgb, var(--accent) 40%, var(--line)), transparent)",
+            }}
+          />
+          <p className="meta mt-4 text-[13.5px] sm:text-[14px] tracking-wide">
+            书籍、文档与页面作品，在线阅读或下载
+          </p>
         </div>
       </section>
 
-      {docs.length === 0 ? (
-        <div
-          className="mt-6 rounded-[20px] px-6 py-14 text-center"
-          style={{ background: "var(--panel)", border: "1px solid var(--line)" }}
-        >
-          <p className="text-[14px] font-medium" style={{ color: "var(--ink-2)" }}>
-            书库还没有内容
-          </p>
-          <p className="meta text-[12.5px] mt-1.5">管理员可在后台「书库管理」发布条目</p>
-        </div>
-      ) : (
-        <div className="mt-6 grid gap-4 sm:grid-cols-2 xl:grid-cols-3">
-          {docs.map((d) => (
-            <DocCard key={d.id} doc={d} href={libraryDocPath(urlStyle, d.slug)} />
-          ))}
-        </div>
-      )}
+      <LibrarySearchGrid docs={docs} urlStyle={settings.url_style} />
     </div>
   );
 }