refactor(marketing): 增加类注释

src/main/java/com/xynet/marketing/controller/merc/PromotionController.java

@@ -15,6 +15,8 @@ import org.springframework.web.bind.annotation.*;
 import java.util.Map;
 
 /**
+ * 商家端促销活动控制器
+ *
  * @author hechunping
  * @date 2025/2/12
  */