fix(backend): 补全多处 Scan/Count 错误未检查，私钥缺失改为 Fatal

- stock.go: ApproveStockIn 入库前库存 Scan 加错误检查
- license.go: Activate 阶段 Count 设备数加错误检查；createTrialLicense
  私钥未配置由静默跳过改为 log.Fatalf，防止生产环境新注册门店无 license
- inventory.go: List 接口两处 Raw Scan 加错误检查并返回 500
- finance.go: ArBalance 汇总 Raw Scan 加错误检查并返回 500

backend/internal/service/license.go

@@ -74,7 +74,9 @@ func (s *LicenseService) Activate(shopID uint64, licenseKey, deviceID, deviceNam
 
 	// New device — enforce max_devices
 	var count int64
-	s.db.Model(&model.LicenseDevice{}).Where("license_id = ?", lic.ID).Count(&count)
+	if err := s.db.Model(&model.LicenseDevice{}).Where("license_id = ?", lic.ID).Count(&count).Error; err != nil {
+		return nil, err
+	}
 	if int(count) >= lic.MaxDevices {
 		return nil, ErrDeviceLimitExceed
 	}
@@ -142,12 +144,11 @@ func (s *LicenseService) Deactivate(shopID uint64, deviceID string) error {
 }
 
 // createTrialLicense 在注册事务中为新门店签发 30 天 trial license。
-// 若私钥未配置则静默跳过（开发/测试环境可不配置私钥）。
+// 私钥未配置时 Fatal，防止生产环境静默跳过导致新注册门店无 license。
 func createTrialLicense(tx *gorm.DB, shopID uint64) {
 	privKey := config.C.License.Ed25519PrivateKey
 	if privKey == "" {
-		log.Printf("[license] Ed25519 private key not configured, skipping trial for shop %d", shopID)
-		return
+		log.Fatalf("[license] Ed25519 private key not configured — cannot issue trial for shop %d; set License.Ed25519PrivateKey in config", shopID)
 	}
 
 	expiresAt := time.Now().Add(30 * 24 * time.Hour)

backend/internal/service/stock.go

@@ -52,10 +52,12 @@ func (s *StockService) ApproveStockIn(shopID, orderID, reviewerID uint64) error
 
 			// 计算入库前库存总量（用于流水记录）
 			var qtyBefore float64
-			tx.Model(&model.Inventory{}).
+			if err := tx.Model(&model.Inventory{}).
 				Where("shop_id = ? AND warehouse_id = ? AND product_id = ? AND deleted_at IS NULL",
 					shopID, warehouseID, productID).
-				Select("COALESCE(SUM(quantity), 0)").Scan(&qtyBefore)
+				Select("COALESCE(SUM(quantity), 0)").Scan(&qtyBefore).Error; err != nil {
+				return err
+			}
 
 			var unitPricePtr *float64
 			if itemCopy.UnitPrice != 0 {
@@ -322,7 +324,7 @@ func (s *StockService) CheckInventoryAvailability(shopID, warehouseID uint64, it
 		have := sumMap[item.ProductID]
 		if have < item.Quantity {
 			var p model.Product
-			s.db.Where("id = ?", item.ProductID).First(&p)
+			s.db.Where("id = ?", item.ProductID).First(&p) //nolint:errcheck — best-effort name lookup for error message
 			name := p.Name
 			if name == "" {
 				name = fmt.Sprintf("商品ID %d", item.ProductID)