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/controller/api/FlowUserController.java

@@ -81,12 +81,13 @@ public class FlowUserController {
         return queryService.detail(schId, instance.getId(), user.getId());
     }
 
-    /** 同意（opinion 可选）——一切审批入口的收敛点 */
+    /** 同意（opinion 可选；多出口节点必须带 edgeName=所选出口名，单出口可省）——一切审批入口的收敛点 */
     @PostMapping("/task/{id}/approve")
     public void approve(BoaUser user, @PathVariable("id") Long id,
                         @RequestBody(required = false) Map<String, String> body) {
         String opinion = body == null ? null : body.get("opinion");
-        taskService.handle(requireSchId(user), id, true, opinion, user.getId());
+        String edgeName = body == null ? null : body.get("edgeName");
+        taskService.handle(requireSchId(user), id, true, opinion, user.getId(), edgeName);
     }
 
     /** 拒绝（opinion 必填） */
@@ -97,6 +98,26 @@ public class FlowUserController {
         taskService.handle(requireSchId(user), id, false, opinion, user.getId());
     }
 
+    /** 退回（targetNodeId 可选=缺省回最近已办节点；opinion 可选） */
+    @PostMapping("/task/{id}/returnBack")
+    public void returnBack(BoaUser user, @PathVariable("id") Long id,
+                           @RequestBody(required = false) Map<String, String> body) {
+        String targetNodeId = body == null ? null : body.get("targetNodeId");
+        String opinion = body == null ? null : body.get("opinion");
+        taskService.returnBack(requireSchId(user), id, targetNodeId, opinion, user.getId());
+    }
+
+    /** 移交（toUserId 必填；reason 可选） */
+    @PostMapping("/task/{id}/transfer")
+    public void transfer(BoaUser user, @PathVariable("id") Long id,
+                         @RequestBody Map<String, Object> body) {
+        Integer toUserId = body.get("toUserId") == null ? null
+                : Integer.valueOf(String.valueOf(body.get("toUserId")));
+        Object reason = body.get("reason");
+        taskService.transfer(requireSchId(user), id, toUserId,
+                reason == null ? null : String.valueOf(reason), user.getId());
+    }
+
     /** 撤回（提交人；仅尚无任务被办理时） */
     @PostMapping("/instance/{id}/withdraw")
     public void withdraw(BoaUser user, @PathVariable("id") Long id) {