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/ad.go

@@ -17,25 +17,25 @@ import (
 const (
 	SettingKeyAdsConfig = "ads_config"
 
-	AdMaxTitleRunes  = 24
-	AdMaxNoteRunes   = 100
-	AdMaxImageShow   = 5
-	AdMaxTextShow    = 6
-	AdMaxActiveShow  = AdMaxImageShow + AdMaxTextShow
-	AdDefaultTitle   = "自助推广"
+	AdMaxTitleRunes = 24
+	AdMaxNoteRunes  = 100
+	AdMaxImageShow  = 5
+	AdMaxTextShow   = 6
+	AdMaxActiveShow = AdMaxImageShow + AdMaxTextShow
+	AdDefaultTitle  = "自助推广"
 )
 
 var (
-	ErrAdNotFound      = errors.New("广告不存在")
-	ErrAdForbidden     = errors.New("无权操作")
-	ErrAdInvalid       = errors.New("广告参数无效")
-	ErrAdCaptcha       = errors.New("验证码错误或已过期")
-	ErrAdDisabled      = errors.New("自助推广暂未开放")
-	ErrAdBadPayment    = errors.New("请选择有效的支付方式")
-	ErrAdBadDuration   = errors.New("请选择有效的投放时长")
-	hexColorRe         = regexp.MustCompile(`^#([0-9a-fA-F]{6})$`)
-	adImageHTTPSRe     = regexp.MustCompile(`(?i)^https://[^\s\\]{1,500}$`)
-	adImageUploadRe    = regexp.MustCompile(`(?i)^/uploads/(ads|images|brand)/[0-9a-f]{32}\.(png|jpe?g|gif|webp)$`)
+	ErrAdNotFound    = errors.New("广告不存在")
+	ErrAdForbidden   = errors.New("无权操作")
+	ErrAdInvalid     = errors.New("广告参数无效")
+	ErrAdCaptcha     = errors.New("验证码错误或已过期")
+	ErrAdDisabled    = errors.New("自助推广暂未开放")
+	ErrAdBadPayment  = errors.New("请选择有效的支付方式")
+	ErrAdBadDuration = errors.New("请选择有效的投放时长")
+	hexColorRe       = regexp.MustCompile(`^#([0-9a-fA-F]{6})$`)
+	adImageHTTPSRe   = regexp.MustCompile(`(?i)^https://[^\s\\]{1,500}$`)
+	adImageUploadRe  = regexp.MustCompile(`(?i)^/uploads/(ads|images|brand)/[0-9a-f]{32}\.(png|jpe?g|gif|webp)$`)
 )
 
 // AdDurationOption 可购时长档位（图片 / 文字广告分别计价）