refactor: 提取 service 层 best-effort 超时常量

- 新增 defaultBETimeout = 5 * time.Second
- 替换 auth/auth_runtime/password_reset/user_service/webhook 中 6 处硬编码 5*time.Second

internal/service/webhook.go

@@ -295,7 +295,7 @@ func (s *WebhookService) recordDelivery(task *deliveryTask, statusCode int, body
 		delivery.DeliveredAt = &now
 	}
 	// 使用带超时的独立 context，防止 DB 写入无限等待
-	writeCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	writeCtx, cancel := context.WithTimeout(context.Background(), defaultBETimeout)
 	defer cancel()
 	_ = s.repo.CreateDelivery(writeCtx, delivery)
 }