feat: add borrowed quantity column and update stocktake export formulas

Co-authored-by: aider (openai/DeepSeek-V3.2-Thinking) <aider@aider.chat>

inventory-backend/app/api/v1/inbound/stock.py

@@ -115,6 +115,22 @@ def clear_draft():
     return jsonify({"message": "Cleared"}), 200
 
 
+@bp.route('/borrowed-quantities', methods=['POST'])
+@permission_required('inventory_stocktake')
+def get_borrowed_quantities():
+    """批量获取借出未还数量"""
+    from app.models.transaction import TransBorrow
+    data = request.json.get('items', [])
+    result = {}
+    for item in data:
+        source = item.get('source_table')
+        stock_id = item.get('stock_id')
+        if source and stock_id is not None:
+            qty = TransBorrow.get_borrowed_quantity(source, stock_id)
+            result[f"{source}_{stock_id}"] = qty
+    return jsonify(result), 200
+
+
 # --- 打印接口 ---
 
 @bp.route('/print/selection', methods=['POST'])