fix(import): 修复导入 504 超时 + 添加上传进度显示

nginx:
- 新增 /api/v1/import/ 专属 location，proxy_read_timeout 延长至 300s

后端:
- ImportInventory 预加载商品/仓库/库存（3 次 bulk query 替代 N+1）
- 批量写 inventory_log（CreateInBatches 替代逐行 Create）

前端:
- settings 导入行：显示"上传 XX%"进度条和"导入数据（Ns）"计时
- Dio 超时设置为 send=120s / receive=300s

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

backend/internal/handler/import.go

@@ -519,23 +519,47 @@ func (h *ImportHandler) ImportInventory(c *gin.Context) {
 	}
 	var res importResult
 
-	// 仓库缓存，只查找不创建
-	warehouseCache := map[string]*uint64{}
+	// 预加载仓库（1 次查询）
+	var warehouses []model.Warehouse
+	h.db.Where("shop_id = ? AND deleted_at IS NULL", shopID).Find(&warehouses)
+	warehouseByName := make(map[string]uint64, len(warehouses))
+	for _, wh := range warehouses {
+		warehouseByName[wh.Name] = wh.ID
+	}
 	findWarehouse := func(name string) *uint64 {
 		if name == "" {
 			return nil
 		}
-		if idPtr, ok := warehouseCache[name]; ok {
-			return idPtr
+		if id, ok := warehouseByName[name]; ok {
+			return &id
 		}
-		var wh model.Warehouse
-		if h.db.Where("shop_id = ? AND name = ? AND deleted_at IS NULL", shopID, name).First(&wh).Error != nil {
-			warehouseCache[name] = nil
-			return nil
+		return nil
+	}
+
+	// 预加载商品（1 次查询）
+	var allProducts []model.Product
+	h.db.Where("shop_id = ? AND deleted_at IS NULL", shopID).Find(&allProducts)
+	productByCode := make(map[string]*model.Product, len(allProducts))
+	productByNSS := make(map[string]*model.Product, len(allProducts))
+	for i := range allProducts {
+		p := &allProducts[i]
+		if p.Code != "" {
+			productByCode[p.Code] = p
 		}
-		id := wh.ID
-		warehouseCache[name] = &id
-		return &id
+		productByNSS[p.Name+"|"+p.Series+"|"+p.Spec] = p
+	}
+
+	// 预加载已有导入库存（1 次查询）
+	var allInvs []model.Inventory
+	h.db.Where("shop_id = ? AND stock_in_item_id IS NULL AND deleted_at IS NULL", shopID).Find(&allInvs)
+	invByKey := make(map[string]*model.Inventory, len(allInvs))
+	for i := range allInvs {
+		inv := &allInvs[i]
+		whID := uint64(0)
+		if inv.WarehouseID != nil {
+			whID = *inv.WarehouseID
+		}
+		invByKey[fmt.Sprintf("%s|%d", inv.ProductCode, whID)] = inv
 	}
 
 	// Dynamic column detection from header row
@@ -561,6 +585,8 @@ func (h *ImportHandler) ImportInventory(c *gin.Context) {
 		}
 	}
 
+	var logsToCreate []model.InventoryLog
+
 	for i, row := range rows[1:] {
 		productName := cell(row, 1)
 		if productName == "" {
@@ -586,20 +612,30 @@ func (h *ImportHandler) ImportInventory(c *gin.Context) {
 		}
 		price, _ := strconv.ParseFloat(priceStr, 64)
 
-		// 只查找商品，不强制创建
-		var prod model.Product
-		if h.db.Where("shop_id = ? AND deleted_at IS NULL AND (code = ? OR (name = ? AND series = ? AND spec = ?))",
-			shopID, productCode, productName, series, spec).First(&prod).Error != nil {
-			// 若找不到则创建
+		// 从缓存查商品，找不到才创建
+		var prod *model.Product
+		if productCode != "" {
+			prod = productByCode[productCode]
+		}
+		if prod == nil {
+			prod = productByNSS[productName+"|"+series+"|"+spec]
+		}
+		if prod == nil {
 			newProd, createErr := findOrCreateProductFn(h.db, shopID, productCode, productName, series, spec)
 			if createErr != nil {
 				res.errors = append(res.errors, fmt.Sprintf("行%d: 商品创建失败: %s", i+2, createErr.Error()))
 				continue
 			}
-			prod = newProd
+			allProducts = append(allProducts, newProd)
+			prod = &allProducts[len(allProducts)-1]
+			if prod.Code != "" {
+				productByCode[prod.Code] = prod
+			}
+			productByNSS[prod.Name+"|"+prod.Series+"|"+prod.Spec] = prod
 		}
 		if unit != "" && prod.Unit == "" {
-			h.db.Model(&prod).Update("unit", unit)
+			h.db.Model(prod).Update("unit", unit)
+			prod.Unit = unit
 		}
 
 		// 解析生产日期
@@ -609,7 +645,6 @@ func (h *ImportHandler) ImportInventory(c *gin.Context) {
 			productionDate = &d
 		}
 
-		// 查找仓库（只查，不创建）
 		whIDPtr := findWarehouse(warehouseName)
 
 		var unitPricePtr *float64
@@ -617,30 +652,25 @@ func (h *ImportHandler) ImportInventory(c *gin.Context) {
 			unitPricePtr = &price
 		}
 
-		productIDCopy := prod.ID
-
-		// Upsert：按商品编号 + 仓库查找已有导入记录，存在则更新，不存在则新建
-		var existing model.Inventory
-		q := h.db.Where("shop_id = ? AND product_code = ? AND stock_in_item_id IS NULL AND deleted_at IS NULL",
-			shopID, prod.Code)
+		// 从缓存查库存记录
+		whIDVal := uint64(0)
 		if whIDPtr != nil {
-			q = q.Where("warehouse_id = ?", *whIDPtr)
-		} else {
-			q = q.Where("warehouse_id IS NULL")
+			whIDVal = *whIDPtr
 		}
-		found := q.First(&existing).Error == nil
+		invKey := fmt.Sprintf("%s|%d", prod.Code, whIDVal)
+		existing := invByKey[invKey]
 
-		if found {
+		if existing != nil {
 			updates := map[string]interface{}{
-				"quantity":        qty,
-				"product_name":    prod.Name,
-				"series":          prod.Series,
-				"spec":            prod.Spec,
-				"unit":            prod.Unit,
-				"warehouse_name":  warehouseName,
-				"supplier_name":   supplierName,
-				"remark":          remark,
-				"deleted_at":      nil,
+				"quantity":       qty,
+				"product_name":   prod.Name,
+				"series":         prod.Series,
+				"spec":           prod.Spec,
+				"unit":           prod.Unit,
+				"warehouse_name": warehouseName,
+				"supplier_name":  supplierName,
+				"remark":         remark,
+				"deleted_at":     nil,
 			}
 			if unitPricePtr != nil {
 				updates["unit_price"] = *unitPricePtr
@@ -651,11 +681,18 @@ func (h *ImportHandler) ImportInventory(c *gin.Context) {
 			if batchNo != "" {
 				updates["batch_no"] = batchNo
 			}
-			if err := h.db.Model(&existing).Updates(updates).Error; err != nil {
+			if err := h.db.Model(existing).Updates(updates).Error; err != nil {
 				res.errors = append(res.errors, fmt.Sprintf("行%d: 库存更新失败: %s", i+2, err.Error()))
 				continue
 			}
+			logsToCreate = append(logsToCreate, model.InventoryLog{
+				ShopID: shopID, WarehouseID: whIDVal, ProductID: prod.ID,
+				Direction: "in", Quantity: qty, QtyBefore: existing.Quantity, QtyAfter: qty,
+				RefType: "import", RefID: 0,
+			})
+			res.updated++
 		} else {
+			productIDCopy := prod.ID
 			inv := model.Inventory{
 				ShopID:         shopID,
 				WarehouseID:    whIDPtr,
@@ -678,32 +715,19 @@ func (h *ImportHandler) ImportInventory(c *gin.Context) {
 				res.errors = append(res.errors, fmt.Sprintf("行%d: 库存写入失败: %s", i+2, err.Error()))
 				continue
 			}
-		}
-
-		// 写流水
-		warehouseID := uint64(0)
-		if whIDPtr != nil {
-			warehouseID = *whIDPtr
-		}
-		qtyBefore := 0.0
-		if found {
-			qtyBefore = existing.Quantity
-			res.updated++
-		} else {
+			invByKey[invKey] = &inv
+			logsToCreate = append(logsToCreate, model.InventoryLog{
+				ShopID: shopID, WarehouseID: whIDVal, ProductID: prod.ID,
+				Direction: "in", Quantity: qty, QtyBefore: 0, QtyAfter: qty,
+				RefType: "import", RefID: 0,
+			})
 			res.imported++
 		}
-		log := model.InventoryLog{
-			ShopID:      shopID,
-			WarehouseID: warehouseID,
-			ProductID:   prod.ID,
-			Direction:   "in",
-			Quantity:    qty,
-			QtyBefore:   qtyBefore,
-			QtyAfter:    qty,
-			RefType:     "import",
-			RefID:       0,
-		}
-		h.db.Create(&log)
+	}
+
+	// 批量写流水
+	if len(logsToCreate) > 0 {
+		h.db.CreateInBatches(&logsToCreate, 100)
 	}
 
 	c.JSON(http.StatusOK, gin.H{