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/auth.go

@@ -30,6 +30,7 @@ const (
 	defaultTOTPChallengeTTL = 5 * time.Minute
 	defaultPasswordMinLen   = 8
 	refreshTokenRetryGrace  = 10 * time.Second
+	defaultBETimeout        = 5 * time.Second  // best-effort 后台操作默认超时
 	MaxUsernameAttempts     = 100 // 最大尝试次数（P1性能优化：减少循环查询）
 	MaxUsernameLength       = 40  // 用户名最大长度
 )
@@ -553,7 +554,7 @@ func (s *AuthService) writeLoginLog(
 				log.Printf("auth: write login log panic recovered, user_id=%v login_type=%d err=%v", userID, loginType, r)
 			}
 		}()
-		bgCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+		bgCtx, cancel := context.WithTimeout(context.Background(), defaultBETimeout)
 		defer cancel()
 		if err := s.loginLogRepo.Create(bgCtx, loginRecord); err != nil {
 			log.Printf("auth: write login log failed, user_id=%v login_type=%d err=%v", userID, loginType, err)
@@ -634,7 +635,7 @@ func (s *AuthService) bestEffortRegisterDevice(ctx context.Context, userID int64
 				log.Printf("auth: register device panic recovered, user_id=%d device_id=%s err=%v", userID, req.DeviceID, r)
 			}
 		}()
-		bgCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+		bgCtx, cancel := context.WithTimeout(context.Background(), defaultBETimeout)
 		defer cancel()
 		_, _ = s.deviceService.CreateDevice(bgCtx, userID, createReq)
 	}()