fix: 完善动态错误指引与发票日期校验（09-05-error-explainability-payment-readiness）

server/tests/unit/routes/workflow.transfer.test.js

@@ -271,6 +271,7 @@ describe("workflow transfer route", () => {
         code: "VALID_001",
         details: expect.objectContaining({
           toApproverId: "target_not_approver",
+          reasonCode: "workflow.transfer_target_ineligible",
         }),
       }),
     );
@@ -306,6 +307,7 @@ describe("workflow transfer route", () => {
       expect(response.json().error.details).toEqual(
         expect.objectContaining({
           toApproverId: "target_not_approver",
+          reasonCode: "workflow.transfer_target_ineligible",
         }),
       );
       expect(tx.workflowTask.update).not.toHaveBeenCalled();
@@ -341,6 +343,7 @@ describe("workflow transfer route", () => {
         code: "VALID_001",
         details: expect.objectContaining({
           workflow: "self_approval_not_allowed",
+          reasonCode: "workflow.self_approval_forbidden",
         }),
       }),
     );