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

backend/service/library_test.go

@@ -18,7 +18,7 @@ func newLibraryTestService(t *testing.T) (*LibraryService, string) {
 	if err != nil {
 		t.Fatalf("open sqlite: %v", err)
 	}
-	if err := db.AutoMigrate(&model.LibraryDoc{}, &model.LibraryFile{}, &model.LibrarySection{}); err != nil {
+	if err := db.AutoMigrate(&model.User{}, &model.LibraryDoc{}, &model.LibraryFile{}, &model.LibrarySection{}); err != nil {
 		t.Fatalf("migrate: %v", err)
 	}
 	dir := t.TempDir()
@@ -45,6 +45,7 @@ func TestLibraryNormalize(t *testing.T) {
 		{"标题为空", func(i *LibraryInput) { i.Title = " " }, "标题不能为空"},
 		{"标题超限", func(i *LibraryInput) { i.Title = strings.Repeat("书", 201) }, "标题不能超过"},
 		{"介绍超限", func(i *LibraryInput) { i.Description = strings.Repeat("介", 20001) }, "介绍不能超过"},
+		{"作者超限", func(i *LibraryInput) { i.Author = strings.Repeat("作", 101) }, "作者不能超过"},
 		{"合法", func(i *LibraryInput) {}, ""},
 	}
 	for _, tc := range cases {
@@ -63,6 +64,58 @@ func TestLibraryNormalize(t *testing.T) {
 	}
 }
 
+func TestLibraryAuthorAndCreator(t *testing.T) {
+	s, _ := newLibraryTestService(t)
+	user := &model.User{Username: "curator", Nickname: "馆长", Avatar: "/a.png"}
+	if err := s.db.Create(user).Error; err != nil {
+		t.Fatalf("create user: %v", err)
+	}
+
+	pub := true
+	doc, err := s.Create(&LibraryInput{
+		Slug: "authored", Title: "署名本", Author: "  鲁迅  ", Published: &pub,
+	}, user.ID)
+	if err != nil {
+		t.Fatalf("create: %v", err)
+	}
+	if doc.Author != "鲁迅" || doc.CreatorID != user.ID {
+		t.Fatalf("作者应裁剪、创建者应落库，got %+v", doc)
+	}
+
+	list, err := s.ListPublished()
+	if err != nil {
+		t.Fatalf("list: %v", err)
+	}
+	if len(list) != 1 || list[0].Author != "鲁迅" {
+		t.Fatalf("列表作者异常: %+v", list)
+	}
+	if c := list[0].Creator; c == nil || c.ID != user.ID || c.Nickname != "馆长" {
+		t.Fatalf("列表创建者摘要异常: %+v", c)
+	}
+
+	detail, err := s.GetPublishedBySlug("authored")
+	if err != nil {
+		t.Fatalf("detail: %v", err)
+	}
+	if detail.Creator == nil || detail.Creator.Username != "curator" {
+		t.Fatalf("详情创建者摘要异常: %+v", detail.Creator)
+	}
+
+	// 作者可清空；更新不改变创建者归属
+	if _, err := s.Update(doc.ID, &LibraryInput{
+		Slug: "authored", Title: "署名本", Author: "", Published: &pub,
+	}); err != nil {
+		t.Fatalf("update: %v", err)
+	}
+	var again model.LibraryDoc
+	if err := s.db.First(&again, doc.ID).Error; err != nil {
+		t.Fatalf("reload: %v", err)
+	}
+	if again.Author != "" || again.CreatorID != user.ID {
+		t.Fatalf("更新后作者/创建者异常: %+v", again)
+	}
+}
+
 func TestLibrarySlugUnique(t *testing.T) {
 	s, _ := newLibraryTestService(t)
 	if _, err := s.Create(&LibraryInput{Slug: "epub-latest", Title: "A"}); err != nil {