feat(stocktake): 重复扫码提示并确认是否修改

问题: 同一个码扫两遍输入两个数，后端 draft/add 直接覆盖，无任何提示
可能误改已盘数量

改进:
- 后端 draft/list 支持 uuid 过滤，可精确查某物料是否已盘
- 扫码弹输入框前，先精确查询该物料是否已盘
- 已盘过 → 弹窗提示『当前实盘为 X，是否修改？』
  确认后预填旧值供修改，取消则不改变

inventory-web/src/views/stock/stocktake/index.vue

@@ -861,15 +861,58 @@ const handleManualInput = async () => {
   }
 }
 
-const openQtyDialog = (item: StockItem) => {
-  currentItem.value = item
-  inputQty.value = item.scanned ? item.qty_actual : 1
-  showQtyDialog.value = true
+const openQtyDialog = async (item: StockItem) => {
+  // ★ 重复扫码检测：精确查该物料是否已在本 session 盘过
+  let existingQty: number | null = null
+  try {
+    const uuidForQuery = item.uuid || item.sku || ''
+    const dupRes: any = await request({
+      url: '/v1/inbound/stock/draft/list',
+      method: 'get',
+      params: { session_id: currentSessionId.value, uuid: uuidForQuery, limit: 1 }
+    })
+    const dupItems = dupRes?.items || dupRes?.data?.items || []
+    if (dupItems.length > 0 && dupItems[0].quantity !== undefined) {
+      existingQty = Number(dupItems[0].quantity)
+    }
+  } catch (e) {
+    // 查询失败不阻断，视为未盘过
+  }
 
-  nextTick(() => {
-    const inputEl = document.querySelector('.qty-dialog input') as HTMLInputElement
-    if(inputEl) inputEl.focus()
-  })
+  if (existingQty !== null) {
+    // 已盘过 → 提示当前值，询问是否修改
+    try {
+      await ElMessageBox.confirm(
+        `⚠️ 【${item.name} × ${item.standard}】已盘过，当前实盘为 ${existingQty}。\n\n是否修改本次盘点的数量？`,
+        '重复扫码提示',
+        {
+          confirmButtonText: '修改数量',
+          cancelButtonText: '取消',
+          type: 'warning'
+        }
+      )
+      // 用户确认修改 → 预填当前值，弹输入框
+      currentItem.value = item
+      inputQty.value = existingQty || 1
+      showQtyDialog.value = true
+      nextTick(() => {
+        const inputEl = document.querySelector('.qty-dialog input') as HTMLInputElement
+        if(inputEl) inputEl.focus()
+      })
+    } catch (e) {
+      // 用户取消，不修改
+      return
+    }
+  } else {
+    // 未盘过 → 正常弹输入框
+    currentItem.value = item
+    inputQty.value = item.scanned ? item.qty_actual : 1
+    showQtyDialog.value = true
+    nextTick(() => {
+      const inputEl = document.querySelector('.qty-dialog input') as HTMLInputElement
+      if(inputEl) inputEl.focus()
+    })
+  }
 }
 
 const handleManualConfirm = () => {