fix(auth): 修复设备首次登录时空指针崩溃问题

在设备不存在分支注册后立即查询设备信息并赋值，避免后续操作解引用空指针
同时增加设备信息空指针保护并完善错误处理

internal/logic/auth/deviceLoginLogic.go

@@ -68,6 +68,7 @@ func (l *DeviceLoginLogic) DeviceLogin(req *types.DeviceLoginRequest) (resp *typ
 	}()
 
 	// Check if device exists by identifier
+	createdNewDevice := false
 	deviceInfo, err := l.svcCtx.UserModel.FindOneDeviceByIdentifier(l.ctx, req.Identifier)
 	if err != nil {
 		if errors.Is(err, gorm.ErrRecordNotFound) {
@@ -76,6 +77,7 @@ func (l *DeviceLoginLogic) DeviceLogin(req *types.DeviceLoginRequest) (resp *typ
 			if err != nil {
 				return nil, err
 			}
+			createdNewDevice = true
 		} else {
 			l.Errorw("query device failed",
 				logger.Field("identifier", req.Identifier),
@@ -95,9 +97,28 @@ func (l *DeviceLoginLogic) DeviceLogin(req *types.DeviceLoginRequest) (resp *typ
 		}
 	}
 
-	// 根据 req 中的UA 更新UA
-	deviceInfo.UserAgent = req.UserAgent
-	_ = l.svcCtx.UserModel.UpdateDevice(l.ctx, deviceInfo)
+	if createdNewDevice {
+		deviceInfo, err = l.svcCtx.UserModel.FindOneDeviceByIdentifier(l.ctx, req.Identifier)
+		if err != nil {
+			l.Errorw("query device after register failed",
+				logger.Field("identifier", req.Identifier),
+				logger.Field("error", err.Error()),
+			)
+			return nil, errors.Wrapf(xerr.NewErrCode(xerr.DatabaseQueryError), "query device after register failed: %v", err.Error())
+		}
+	}
+
+	if deviceInfo != nil {
+		deviceInfo.UserAgent = req.UserAgent
+		if err := l.svcCtx.UserModel.UpdateDevice(l.ctx, deviceInfo); err != nil {
+			l.Errorw("update device failed",
+				logger.Field("user_id", userInfo.Id),
+				logger.Field("identifier", req.Identifier),
+				logger.Field("error", err.Error()),
+			)
+			return nil, errors.Wrapf(xerr.NewErrCode(xerr.DatabaseUpdateError), "update device failed: %v", err.Error())
+		}
+	}
 
 	// Generate session id
 	sessionId := uuidx.NewUUID().String()