fix: 添加缺失的 DepartmentMapper 依赖

backend/src/main/java/com/designhub/service/TaskService.java

@@ -59,6 +59,7 @@ public class TaskService {
     private final com.designhub.mapper.TaskItemMapper taskItemMapper;
     private final DeptMonthlyScoreService deptMonthlyScoreService;
     private final SystemConfigService systemConfigService;
+    private final com.designhub.mapper.DepartmentMapper departmentMapper;
 
     /**
      * 创建任务