fix: R.failed 参数类型错误，改为 R.failed(-1, msg)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

car-wash-miniapp/src/main/java/com/kym/miniapp/controller/WeixinMPController.java

@@ -85,7 +85,7 @@ public class WeixinMPController {
             return R.success("同步完成");
         } catch (WxErrorException e) {
             log.error("手动同步公众号用户失败", e);
-            return R.failed("同步失败: " + e.getMessage());
+            return R.failed(-1, "同步失败: " + e.getMessage());
         }
     }