feat(borrow): 借库未归还直接报废功能（关联报废单流程）

后端:
- trans_service 新增 scrap_borrow 方法：未归还借用标记为 scrapped，
  扣减总库存 stock_quantity（可用已在借出时冻结），生成 TransScrap 报废记录
- transactions.py 新增 POST /borrow/scrap 接口（复用 op_return:operation 权限，库管/主管可操作）
- scrap.py query_records 支持 trans_borrow 来源的物料名解析 + 行级隔离

前端:
- records.vue 未归还记录新增「报废」按钮（库管/主管可见）
- 报废弹窗：勾选明细 + 填报废原因 + 二次确认
- 状态显示新增「已报废」标签；整单所有明细报废时标记为 scrapped

inventory-backend/app/services/trans_service.py

@@ -327,6 +327,86 @@ class TransService:
             db.session.rollback()
             raise e
 
+    @staticmethod
+    def scrap_borrow(record_ids, operator_name='System', reason=''):
+        """
+        借库未归还直接报废（关联报废单流程）
+
+        适用场景：借出的物品确认丢失/损坏/无法归还，库管/主管手动报废。
+        - 该笔借用不再追讨归还，从借还记录中标记为已报废
+        - 生成一条 TransScrap 报废记录（关联 trans_borrow）
+        - 总库存 stock_quantity 扣减（该物品确认损失）；可用库存已在借出时冻结，无需重复扣
+
+        Args:
+            record_ids: TransBorrow 记录ID列表
+            operator_name: 操作人
+            reason: 报废原因
+
+        Returns:
+            {count: 报废条数}
+        """
+        from app.models.transaction import TransScrap
+
+        if not record_ids:
+            raise ValueError('请选择要报废的借出记录')
+        if not reason:
+            raise ValueError('请填写报废原因')
+
+        model_map = {'stock_buy': StockBuy, 'stock_semi': StockSemi, 'stock_product': StockProduct}
+        created_records = []
+        scraped_count = 0
+
+        try:
+            for rid in record_ids:
+                record = TransBorrow.query.with_for_update().get(rid)
+                if not record:
+                    continue
+                # 仅未归还的借用可报废
+                if record.is_returned:
+                    continue
+                pending_qty = float(record.quantity) - float(record.returned_quantity or 0)
+                if pending_qty <= 0:
+                    continue
+
+                # 1. 标记借用记录为已报废（不再追讨归还）
+                record.is_returned = True
+                record.status = 'scrapped'
+                record.return_time = datetime.now()
+                record.return_operator = operator_name
+
+                # 2. 扣减总库存（该物品确认损失）；可用库存已在借出时冻结
+                ModelClass = model_map.get(record.source_table)
+                if ModelClass:
+                    stock = ModelClass.query.with_for_update().get(record.stock_id)
+                    if stock:
+                        stock.stock_quantity = float(stock.stock_quantity or 0) - pending_qty
+                        # 防止负库存
+                        if stock.stock_quantity < 0:
+                            stock.stock_quantity = 0
+
+                # 3. 创建报废记录
+                scrap_record = TransScrap(
+                    sku=record.sku,
+                    source_table='trans_borrow',   # 标识来源为借出转报废
+                    stock_id=record.id,
+                    quantity=pending_qty,
+                    reason=f"[借库报废] {reason}",
+                    operator_name=operator_name,
+                    approval_status='approved',
+                    cost_at_scrap=0,
+                    total_loss=0
+                )
+                db.session.add(scrap_record)
+                created_records.append(scrap_record)
+                scraped_count += 1
+
+            db.session.commit()
+            return {'count': scraped_count}
+
+        except Exception as e:
+            db.session.rollback()
+            raise e
+
     @staticmethod
     def get_records(page=1, limit=10, status='all', keyword=None, search_type='all'):
         """