feat: 引擎多出口路由/退回/移交/或签补齐 + 定义 layout 坐标

- 多出口：FlwTask 增 edge_name 列（sql/20260916），FlwTaskRepository.claimAndFinish
  同步落列；FlowTaskService.handle 出度>1 时 edgeName 必填；FlowEngine.continueAdvance
  按 edge name 选路（单出口原路径逐字节兼容，未命中不推进）；FlowAdvanceService/
  FlowNodeAdvanceListener 透传；BranchScope 从 FlowEngine 提取
- DefValidator：多出口出口命名必填且同节点唯一；跨分支连线发布期明确拒绝
- 退回 POST /task/{id}/returnBack：默认退主管线最近已批节点，精确失效当前节点待办，
  split 幂等 upsert 使退回重走并行段不撞 flw_branch uk
- 移交 POST /task/{id}/transfer：TRANSFERRED(5)+新建待办，AssigneeResolver.requireUserName
- 或签 ANY 补齐：首个同意失效同节点兄弟待办
- 已办口径/撤回守卫：status in (1,2,4,5)；新事件 flow.returned/flow.transferred
- FlowDiagramService：EdgeVo.name/NodeVo.state/DiagramVo.layout，办件图状态计算
- 新 IT：多出口×3、ANY 或签、退回重走并行段、退回/移交/撤回

mvn test 84/84 绿

src/main/java/com/yunhai/flowcenter/notify/UserMsgNotifier.java

@@ -40,6 +40,12 @@ public class UserMsgNotifier {
             case TASK_HANDLED:
                 notifyTaskHandled(event);
                 break;
+            case RETURNED:
+                notifyReturned(event);
+                break;
+            case TRANSFERRED:
+                notifyTaskCreated(event);
+                break;
             case COMPLETED:
             case REJECTED:
             case WITHDRAWN:
@@ -80,6 +86,36 @@ public class UserMsgNotifier {
                 Collections.singletonList(task.getAssigneeId()), -1);
     }
 
+    /**
+     * 退回：通知被退回节点的全部新待办人（RETURNED 事件 data.targetNodeIds 由服务层带上——
+     * 退回重建任务在事件发布前已提交，这里按节点查待办即可）；todo 角标由 notifyTaskCreated
+     * 通用链路在引擎重建任务时已发过，这里只补一条带退回意见的消息。
+     */
+    private void notifyReturned(FlowEvent event) {
+        FlwInstance instance = instanceOf(event.getInstanceId());
+        if (instance == null || event.getData() == null) {
+            return;
+        }
+        Object fromNode = event.getData().get("fromNodeName");
+        Object opinion = event.getData().get("opinion");
+        StringBuilder content = new StringBuilder("「").append(safe(instance.getBizTitle())).append("」")
+                .append("被退回（").append(fromNode == null ? "" : fromNode).append("）");
+        if (opinion != null && !String.valueOf(opinion).isEmpty()) {
+            content.append("，意见：").append(opinion);
+        }
+        java.util.List<Integer> targets = event.getData().get("targetUserIds") == null
+                ? Collections.emptyList()
+                : (java.util.List<Integer>) event.getData().get("targetUserIds");
+        if (targets.isEmpty()) {
+            return;
+        }
+        userMsgClient.sendUserMsg(instance.getSchId().intValue(), targets, 1,
+                "flow.returned", String.valueOf(instance.getId()),
+                "办件被退回：" + safe(instance.getBizTitle()), content.toString(),
+                "/instance/" + instance.getId(),
+                "returned:" + instance.getId() + ":" + instance.getVersion(), 30);
+    }
+
     private void notifyResult(FlowEvent event) {
         FlwInstance instance = instanceOf(event.getInstanceId());
         if (instance == null) {