fix: add load_factor upper bound validation to BulkUpdateAccounts

backend/internal/service/admin_service.go

@@ -1635,8 +1635,14 @@ func (s *adminServiceImpl) BulkUpdateAccounts(ctx context.Context, input *BulkUp
 		repoUpdates.RateMultiplier = input.RateMultiplier
 	}
 	if input.LoadFactor != nil {
+		if *input.LoadFactor <= 0 {
+			repoUpdates.LoadFactor = nil // 0 或负数表示清除
+		} else if *input.LoadFactor > 10000 {
+			return nil, errors.New("load_factor must be <= 10000")
+		} else {
 			repoUpdates.LoadFactor = input.LoadFactor
 		}
+	}
 	if input.Status != "" {
 		repoUpdates.Status = &input.Status
 	}