fix(import): 库存列头动态识别 + 格式不匹配诊断信息

商品名称/编号/系列/规格/单位列索引从固定 0-4 改为从表头动态识别，
支持更多列名变体（品名/名称/货品名称/编码等）。

全部跳过时在 errors 中返回识别到的表头，便于诊断列格式问题。

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/handler/import.go

@@ -563,21 +563,32 @@ func (h *ImportHandler) ImportInventory(c *gin.Context) {
 	}
 
 	// Dynamic column detection from header row
+	colProductCode, colProductName, colSeries, colSpec, colUnit := 0, 1, 2, 3, 4
 	colQty, colPrice, colProductionDate, colBatchNo, colWarehouse, colSupplier, colRemark := 5, 6, 8, 9, 11, 13, 15
 	if len(rows) > 0 {
 		for j, h := range rows[0] {
 			switch strings.TrimSpace(h) {
-			case "库存数量", "数量":
+			case "商品编号", "商品编码", "编号", "编码", "商品条码":
+				colProductCode = j
+			case "商品名称", "品名", "名称", "货品名称":
+				colProductName = j
+			case "系列", "品牌系列":
+				colSeries = j
+			case "规格", "规格型号":
+				colSpec = j
+			case "单位":
+				colUnit = j
+			case "库存数量", "数量", "库存":
 				colQty = j
-			case "单价":
+			case "单价", "进价", "采购单价":
 				colPrice = j
-			case "生产日期":
+			case "生产日期", "生产年月":
 				colProductionDate = j
 			case "批次", "批次号":
 				colBatchNo = j
-			case "所在仓库", "仓库":
+			case "所在仓库", "仓库", "库位":
 				colWarehouse = j
-			case "供应商":
+			case "供应商", "供应商名称":
 				colSupplier = j
 			case "备注":
 				colRemark = j
@@ -585,19 +596,22 @@ func (h *ImportHandler) ImportInventory(c *gin.Context) {
 		}
 	}
 
+	// 如果没有匹配到任何列头，返回诊断信息
+	detectedHeader := strings.Join(rows[0], " | ")
+
 	var logsToCreate []model.InventoryLog
 
 	for i, row := range rows[1:] {
-		productName := cell(row, 1)
+		productName := cell(row, colProductName)
 		if productName == "" {
 			res.skipped++
 			continue
 		}
 
-		productCode := cell(row, 0)
-		series := cell(row, 2)
-		spec := cell(row, 3)
-		unit := cell(row, 4)
+		productCode := cell(row, colProductCode)
+		series := cell(row, colSeries)
+		spec := cell(row, colSpec)
+		unit := cell(row, colUnit)
 		qtyStr := cell(row, colQty)
 		priceStr := cell(row, colPrice)
 		productionDateStr := cell(row, colProductionDate)
@@ -730,6 +744,12 @@ func (h *ImportHandler) ImportInventory(c *gin.Context) {
 		h.db.CreateInBatches(&logsToCreate, 100)
 	}
 
+	// 全部跳过说明列格式不匹配，返回诊断信息
+	if res.imported == 0 && res.updated == 0 && res.skipped > 0 && len(res.errors) == 0 {
+		res.errors = append(res.errors,
+			fmt.Sprintf("所有行商品名称列为空，可能列格式不匹配。识别到的表头：%s", detectedHeader))
+	}
+
 	c.JSON(http.StatusOK, gin.H{
 		"imported": res.imported,
 		"updated":  res.updated,