feat(parity): align Chatwoot 4.15.1 contracts

backend/internal/handler/api/v1/article_handler.go

@@ -853,11 +853,13 @@ func articlePayload(article *model.Article) gin.H {
 }
 
 func articleCategoryPayload(article *model.Article) gin.H {
-	payload := gin.H{"id": article.CategoryID, "name": nil, "slug": nil, "locale": nil}
+	payload := gin.H{"id": article.CategoryID, "name": nil, "slug": nil, "locale": nil, "icon": nil, "icon_color": nil}
 	if article.Category != nil {
 		payload["name"] = article.Category.Name
 		payload["slug"] = article.Category.Slug
 		payload["locale"] = article.Category.Locale
+		payload["icon"] = article.Category.Icon
+		payload["icon_color"] = article.Category.IconColor
 	}
 	return payload
 }