fix(claim): 透出 affiliate_dash 上游错误，便于排查提交 UID 失败

上游 4xx 不再一律打成 502 兜底文案；affiliate_dash 依赖错误优先展示真实 message。

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/backend/src/utils/http.ts

@@ -29,12 +29,16 @@ export function buildSuccessPayload(data: unknown, msg: string = 'ok') {
 
 export function buildErrorPayload(error: unknown, fallbackMessage: string) {
   const classification = classifyRouteError(error)
-  const message =
-    classification.statusCode >= 500
+  const errorMessage = error instanceof Error ? String(error.message || '').trim() : ''
+  // 依赖方错误（如 affiliate_dash）即使映射为 5xx，也优先透出上游可读原因。
+  const preferUpstreamMessage =
+    errorMessage &&
+    (classification.statusCode < 500 || classification.errorCode.startsWith('affiliate_dash'))
+  const message = preferUpstreamMessage
+    ? errorMessage
+    : classification.statusCode >= 500
       ? fallbackMessage || '服务内部错误'
-      : error instanceof Error
-        ? error.message
-        : fallbackMessage
+      : errorMessage || fallbackMessage
 
   return {
     code: 1,