perf(workflow): 优化工作流任务查询性能

- 添加显式字段映射避免全量数据加载
- 减少数据库查询的数据传输量
- 提升工作流实例任务列表加载速度

OpenAuth.App/workflow/WorkflowEngineApp.cs

@@ -1176,6 +1176,17 @@ public class WorkflowEngineApp : SqlSugarBaseApp<SysCategoryType, SugarDbContext
             .Queryable<ZyFlowWorkitem>()
             .Where(w => w.InstanceId == instance.InstanceId)
             .OrderByDescending(w => w.WorkitemId)
+            .Select(w => new
+                ZyFlowWorkitem
+                {
+                    WorkitemId = w.WorkitemId,
+                    Comment = w.Comment,
+                    Status = w.Status,
+                    ReceiveTime = w.ReceiveTime,
+                    HandleTime = w.HandleTime,
+                    HandlerName = w.HandlerName,
+                    NodeName = w.NodeName
+                })
             .ToList();
 
         var illegalConstructionAssessment = _sqlSugar