feat: 完成错误原因合同与付款就绪提示（09-05-error-explainability-payment-readiness）

client/tests/e2e/r103-cross-page-ui-consistency.spec.ts

@@ -542,7 +542,7 @@ async function mockApis(page: Page, options: { roleCodes?: string[] } = {}) {
             error: {
               code: "VALID_001",
               message: "参数校验失败",
-              details: { file: "unsupported_type" },
+              details: { file: "unsupported_type", reasonCode: "purchase_attachment.unsupported_type" },
             },
           }),
         });