fix(backend): resolve DetachedInstanceError in audit_log, add pessimistic locks for stock adjustments, and eliminate N+1 queries with eager loading

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

@@ -132,7 +132,8 @@ def create():
     if not StockModel:
         return jsonify({'code': 400, 'msg': '无效的库存类型'}), 400
 
-    stock = StockModel.query.get(stock_id)
+    # ★ 修复并发冲突：使用悲观锁锁定行，防止多人同时修改导致的数据覆盖
+    stock = StockModel.query.filter(StockModel.id == stock_id).with_for_update().first()
     if not stock:
         return jsonify({'code': 404, 'msg': '库存记录不存在'}), 404