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/handler/finance.go

@@ -173,7 +173,7 @@ func (h *FinanceHandler) Summary(c *gin.Context) {
 		TotalAmount float64 `json:"total_amount"`
 	}
 	var rows []row
-	h.db.Raw(`
+	if err := h.db.Raw(`
 		SELECT f.partner_id,
 		       COALESCE(p.name, '') AS partner_name,
 		       f.type,
@@ -186,7 +186,10 @@ func (h *FinanceHandler) Summary(c *gin.Context) {
 		  AND f.status = 'open'
 		GROUP BY f.partner_id, f.type
 		ORDER BY total_amount DESC
-	`, shopID).Scan(&rows)
+	`, shopID).Scan(&rows).Error; err != nil {
+		util.RespondError(c, http.StatusInternalServerError, "QUERY_ERROR", "查询失败")
+		return
+	}
 
 	util.RespondSuccess(c, rows)
 }

backend/internal/handler/inventory.go

@@ -87,7 +87,10 @@ func (h *InventoryHandler) List(c *gin.Context) {
 		WHERE ` + baseWhere
 
 	var total int64
-	h.db.Raw(countSQL, args...).Scan(&total)
+	if err := h.db.Raw(countSQL, args...).Scan(&total).Error; err != nil {
+		util.RespondError(c, http.StatusInternalServerError, "QUERY_ERROR", "查询失败")
+		return
+	}
 
 	// Data query
 	dataSQL := `
@@ -119,7 +122,10 @@ func (h *InventoryHandler) List(c *gin.Context) {
 	dataArgs := append(args, pageSize, (page-1)*pageSize)
 
 	var rows []inventoryRow
-	h.db.Raw(dataSQL, dataArgs...).Scan(&rows)
+	if err := h.db.Raw(dataSQL, dataArgs...).Scan(&rows).Error; err != nil {
+		util.RespondError(c, http.StatusInternalServerError, "QUERY_ERROR", "查询失败")
+		return
+	}
 
 	c.JSON(http.StatusOK, gin.H{"data": rows, "total": total, "page": page, "page_size": pageSize})
 }