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/[slug]/page.tsx

@@ -9,13 +9,14 @@ import { getPublicSettingsCached } from "@/lib/serverData";
 import MarkdownBody from "@/components/MarkdownBody";
 import { SiteDocMasthead } from "@/components/site-doc";
 import { requestCanonical } from "@/lib/canonicalMeta";
-import { libraryDocPath, libraryDocReadPath } from "@/lib/urlStyle";
+import { libraryDocPath, libraryDocReadPath, userPath } from "@/lib/urlStyle";
 import { webPageJsonLd } from "@/lib/jsonLd";
 import JsonLd from "@/components/JsonLd";
 import { estimateReadingMinutes } from "@/lib/toc";
 import { groupSections } from "@/lib/librarySections";
 import LightboxImage from "@/components/LightboxImage";
 import AdaptiveCoverSlot from "@/components/AdaptiveCoverSlot";
+import Avatar from "@/components/Avatar";
 
 interface PageProps {
   params: Promise<{ slug: string }>;
@@ -64,23 +65,27 @@ function ExtChip({ ext }: { ext: string }) {
 function FileRow({ f }: { f: LibraryFileItem }) {
   return (
     <div
-      className="rounded-xl px-4 py-3"
+      className="rounded-xl px-3 py-2.5"
       style={{ border: "1px solid var(--line)", background: "var(--bg)" }}
     >
-      <div className="flex flex-wrap items-center gap-x-3 gap-y-1.5">
+      {/* 紧凑两行式：适配左栏窄列，文件名过长截断（悬停可见全名），避免被压成逐字换行 */}
+      <div className="flex items-center gap-2 min-w-0">
         <ExtChip ext={f.ext} />
         <span
-          className="text-[13.5px] font-medium min-w-0 break-all"
+          className="text-[13px] font-medium min-w-0 truncate"
           style={{ color: "var(--ink)" }}
+          title={f.name}
         >
           {f.name}
         </span>
-        <span className="meta text-[11.5px]">
+      </div>
+      <div className="mt-2 flex items-center justify-between gap-2">
+        <span className="meta text-[11.5px] shrink-0">
           {formatSize(f.size)} · {f.download_count} 次下载
         </span>
         <a
           href={`/api/library/files/${f.id}/download`}
-          className="btn btn-sm btn-primary ml-auto inline-flex items-center gap-1.5 shrink-0"
+          className="btn btn-sm btn-primary inline-flex items-center gap-1.5 shrink-0"
         >
           <Download size={13} /> 下载
         </a>
@@ -159,12 +164,23 @@ export default async function LibraryDocPage({ params }: PageProps) {
           {/* 横版封面（宽>高且足够大）：全宽置于内容上方；竖版或过小的横版图时此槽位不渲染。
               小图不强行放大占满全宽：max-w-full 下保持自然尺寸，容器随内容收缩并水平居中 */}
           {d.cover_url ? (
-            <AdaptiveCoverSlot orientation="landscape" src={d.cover_url}>
+            <AdaptiveCoverSlot
+              orientation="landscape"
+              src={d.cover_url}
+              naturalWidth={d.cover_width}
+              naturalHeight={d.cover_height}
+            >
               <div
                 className="mt-6 w-fit max-w-full mx-auto overflow-hidden rounded-2xl"
                 style={{ border: "1px solid var(--line)" }}
               >
-                <LightboxImage src={d.cover_url} alt={d.title} className="max-w-full h-auto block" />
+                <LightboxImage
+                  src={d.cover_url}
+                  alt={d.title}
+                  className="max-w-full h-auto block"
+                  variantWidths={[768, 1080, 1920]}
+                  sizes="(max-width:1280px) 92vw, 1080px"
+                />
               </div>
             </AdaptiveCoverSlot>
           ) : null}
@@ -175,18 +191,40 @@ export default async function LibraryDocPage({ params }: PageProps) {
               {d.cover_url ? (
                 // 竖版封面（长>宽）及过小的横版封面：按图片自然比例显示在左栏；
                 // 小图不强行放大占满：保持自然尺寸，在槽位最大区域内水平垂直居中
-                <AdaptiveCoverSlot orientation="portrait" src={d.cover_url}>
+                <AdaptiveCoverSlot
+                  orientation="portrait"
+                  src={d.cover_url}
+                  naturalWidth={d.cover_width}
+                  naturalHeight={d.cover_height}
+                >
                   <div
                     className="w-fit max-w-full mx-auto overflow-hidden rounded-2xl"
                     style={{ border: "1px solid var(--line)" }}
                   >
-                    <LightboxImage src={d.cover_url} alt={d.title} className="max-w-full h-auto block" />
+                    <LightboxImage
+                      src={d.cover_url}
+                      alt={d.title}
+                      className="max-w-full h-auto block"
+                      variantWidths={[384, 768]}
+                      sizes="(max-width:1023px) 92vw, 340px"
+                    />
                   </div>
                 </AdaptiveCoverSlot>
               ) : (
                 <CoverFallback title={d.title} />
               )}
               <dl className="mt-4 flex flex-col gap-2 text-[13px]">
+                {d.author ? (
+                  <div className="flex items-start justify-between gap-3">
+                    <dt className="meta shrink-0">作者</dt>
+                    <dd
+                      className="font-semibold text-right min-w-0"
+                      style={{ color: "var(--ink)" }}
+                    >
+                      {d.author}
+                    </dd>
+                  </div>
+                ) : null}
                 <div className="flex items-center justify-between">
                   <dt className="meta">章节数</dt>
                   <dd className="tabular-nums font-semibold" style={{ color: "var(--ink)" }}>
@@ -199,6 +237,30 @@ export default async function LibraryDocPage({ params }: PageProps) {
                     {d.files.length}
                   </dd>
                 </div>
+                {d.creator ? (
+                  <div className="flex items-center justify-between gap-2">
+                    <dt className="meta shrink-0">创建者</dt>
+                    <dd className="min-w-0">
+                      <Link
+                        href={userPath(urlStyle, d.creator.id)}
+                        className="inline-flex items-center gap-1.5 min-w-0"
+                        title={`@${d.creator.username}`}
+                      >
+                        <Avatar
+                          size={20}
+                          name={d.creator.nickname || d.creator.username}
+                          src={d.creator.avatar}
+                        />
+                        <span
+                          className="text-[12.5px] font-medium truncate max-w-[9rem]"
+                          style={{ color: "var(--ink)" }}
+                        >
+                          {d.creator.nickname || d.creator.username}
+                        </span>
+                      </Link>
+                    </dd>
+                  </div>
+                ) : null}
               </dl>
               {chapterCount > 0 ? (
                 <Link
@@ -208,9 +270,28 @@ export default async function LibraryDocPage({ params }: PageProps) {
                   <BookOpen size={15} aria-hidden /> 开始阅读
                 </Link>
               ) : null}
+
+              {/* 附件下载紧跟阅读按钮：左栏桌面端 sticky 常驻，移动端排在介绍之前，
+                  避免介绍过长时用户需要长距离滚动寻找下载入口 */}
+              {d.files.length > 0 ? (
+                <section id="files" className="mt-5 scroll-mt-24">
+                  <h2
+                    className="text-[13.5px] font-bold inline-flex items-center gap-2"
+                    style={{ color: "var(--ink)" }}
+                  >
+                    <Download size={14} style={{ color: "var(--accent)" }} aria-hidden />
+                    附件下载（{d.files.length}）
+                  </h2>
+                  <div className="mt-2.5 flex flex-col gap-2">
+                    {d.files.map((f) => (
+                      <FileRow key={f.id} f={f} />
+                    ))}
+                  </div>
+                </section>
+              ) : null}
             </aside>
 
-            {/* 右栏：介绍 + 附件 */}
+            {/* 右栏：介绍（附件下载已移至左栏阅读按钮下方） */}
             <div className="mt-6 lg:mt-0 min-w-0">
               <section>
                 <h2
@@ -228,25 +309,6 @@ export default async function LibraryDocPage({ params }: PageProps) {
                   )}
                 </div>
               </section>
-
-              <section id="files" className="mt-9 scroll-mt-24">
-                <h2
-                  className="text-[15px] font-bold inline-flex items-center gap-2"
-                  style={{ color: "var(--ink)" }}
-                >
-                  <Download size={15} style={{ color: "var(--accent)" }} aria-hidden />
-                  附件下载（{d.files.length}）
-                </h2>
-                {d.files.length === 0 ? (
-                  <p className="meta text-[12.5px] mt-3">暂无附件</p>
-                ) : (
-                  <div className="mt-3 flex flex-col gap-2.5">
-                    {d.files.map((f) => (
-                      <FileRow key={f.id} f={f} />
-                    ))}
-                  </div>
-                )}
-              </section>
             </div>
           </div>
         </article>