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/components/markdown/MdImage.tsx

@@ -2,27 +2,33 @@
 
 import { useState, useCallback, type ImgHTMLAttributes } from "react";
 import ImageLightbox, { type LightboxItem } from "./ImageLightbox";
+import { isOwnImage, variantURL, widthSrcSet } from "@/lib/responsiveImage";
 
 type MdImageProps = ImgHTMLAttributes<HTMLImageElement>;
 
+/** 图箱收集的原图地址：data-full 优先（页面显示变体时仍指向原图） */
+function fullSrc(el: HTMLImageElement): string {
+	return el.dataset.full || el.currentSrc || el.getAttribute("src") || "";
+}
+
 function collectGallery(from: HTMLImageElement): { items: LightboxItem[]; index: number } {
-  const root = from.closest(".prose-content");
-  const nodes = root
-    ? Array.from(root.querySelectorAll<HTMLImageElement>("img.md-content-img[src]"))
-    : [from];
-  const items: LightboxItem[] = nodes
-    .map((el) => ({
-      src: el.currentSrc || el.getAttribute("src") || "",
-      alt: el.dataset.caption || undefined,
-    }))
-    .filter((it) => !!it.src);
-  const selfSrc = from.currentSrc || from.getAttribute("src") || "";
-  let index = items.findIndex((it) => it.src === selfSrc);
-  if (index < 0) index = 0;
-  if (items.length === 0 && selfSrc) {
-    return { items: [{ src: selfSrc, alt: from.dataset.caption || undefined }], index: 0 };
-  }
-  return { items, index };
+	const root = from.closest(".prose-content");
+	const nodes = root
+		? Array.from(root.querySelectorAll<HTMLImageElement>("img.md-content-img[src]"))
+		: [from];
+	const items: LightboxItem[] = nodes
+		.map((el) => ({
+			src: fullSrc(el),
+			alt: el.dataset.caption || undefined,
+		}))
+		.filter((it) => !!it.src);
+	const selfSrc = fullSrc(from);
+	let index = items.findIndex((it) => it.src === selfSrc);
+	if (index < 0) index = 0;
+	if (items.length === 0 && selfSrc) {
+		return { items: [{ src: selfSrc, alt: from.dataset.caption || undefined }], index: 0 };
+	}
+	return { items, index };
 }
 
 /** Markdown 正文图片：点击进入图箱，同文多图可切换 */
@@ -42,6 +48,9 @@ export default function MdImage({ src, alt, title, className, ...rest }: MdImage
   const provided = (typeof alt === "string" ? alt.trim() : "") || (typeof title === "string" ? title.trim() : "");
   const imgAlt = provided || "图片";
 
+  // 同源图（本地 /uploads 或 /api/media 对象）才可走变体端点；外链图原样加载
+  const isLocalSrc = typeof src === "string" && isOwnImage(src);
+
   // 抖音表情（/emoji/ 路径）：行内小图，不进图箱、不带 caption；
   // alt 由 expandDyEmojiShortcodes 产出（"dy:<key>"），悬停 title 显示其短代码
   const isEmoji = typeof src === "string" && src.includes("/emoji/");
@@ -78,9 +87,13 @@ export default function MdImage({ src, alt, title, className, ...rest }: MdImage
       {/* eslint-disable-next-line @next/next/no-img-element */}
       <img
         {...rest}
-        src={src}
+        // 同源图（/uploads、/api/media）页面内走宽度变体；外链图保持原 src 不回归
+        src={isLocalSrc ? variantURL(src, 512) : src}
+        srcSet={isLocalSrc ? widthSrcSet(src, [512, 768, 1080, 1536]) : undefined}
+        sizes={isLocalSrc ? "(max-width:768px) 92vw, 720px" : undefined}
         alt={imgAlt}
         data-caption={provided || undefined}
+        data-full={src}
         title={title}
         className={`md-content-img${className ? ` ${className}` : ""}`}
         loading="lazy"