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/lib/widgetCode.test.ts

@@ -1,6 +1,6 @@
 import assert from "node:assert/strict";
 import { describe, it } from "node:test";
-import { mergeWidgetCode, parseMixedWidgetCode, scopeWidgetCss } from "./widgetCode.ts";
+import { mergeWidgetCode, parseMixedWidgetCode } from "./widgetCode.ts";
 
 describe("parseMixedWidgetCode", () => {
   it("拆分混写的 style/script 段", () => {
@@ -45,58 +45,3 @@ describe("mergeWidgetCode", () => {
     assert.equal(mergeWidgetCode({ html: "hi", css: "", js: "" }), "hi");
   });
 });
-
-describe("scopeWidgetCss", () => {
-  const p = ".j13-widget-7";
-
-  it("普通规则加前缀", () => {
-    assert.equal(scopeWidgetCss(".a { color: red; }", 7), `${p} .a { color: red; }`);
-  });
-
-  it("选择器列表逐个前缀，括号内逗号不分割", () => {
-    assert.equal(
-      scopeWidgetCss(".a, .b {}", 7),
-      `${p} .a, ${p} .b {}`
-    );
-    assert.equal(
-      scopeWidgetCss(':is(.a, .b) { color: red }', 7),
-      `${p} :is(.a, .b) { color: red }`
-    );
-  });
-
-  it("root/body 选择器替换为容器本身", () => {
-    assert.equal(scopeWidgetCss(":root { --x: 1; }", 7), `${p} { --x: 1; }`);
-    assert.equal(scopeWidgetCss("body { margin: 0 }", 7), `${p} { margin: 0 }`);
-    assert.equal(scopeWidgetCss("body .card {}", 7), `${p} .card {}`);
-  });
-
-  it("容器自身伪类紧贴前缀", () => {
-    assert.equal(scopeWidgetCss(":hover { opacity: .8 }", 7), `${p}:hover { opacity: .8 }`);
-  });
-
-  it("@media 内层前缀化，头部原样", () => {
-    assert.equal(
-      scopeWidgetCss("@media (min-width: 10px) { .a {} }", 7),
-      `@media (min-width: 10px) { ${p} .a {} }`
-    );
-  });
-
-  it("@keyframes 原样保留", () => {
-    const css = "@keyframes spin { from { opacity: 0 } to { opacity: 1 } }";
-    assert.equal(scopeWidgetCss(css, 7), css);
-  });
-
-  it("@import 语句原样保留", () => {
-    assert.equal(
-      scopeWidgetCss('@import url("a.css"); .a {}', 7),
-      '@import url("a.css"); .j13-widget-7 .a {}'
-    );
-  });
-
-  it("注释与字符串内的花括号不干扰配对", () => {
-    assert.equal(
-      scopeWidgetCss("/* { nope } */ .a::after { content: \"{\" }", 7),
-      `/* { nope } */ ${p} .a::after { content: "{" }`
-    );
-  });
-});