feat(shopping): relation product sur ListItem

backend/app/models/shopping.py

@@ -1,6 +1,7 @@
 import uuid
 from datetime import datetime, date
 from decimal import Decimal
+from typing import Optional
 from sqlalchemy import String, Text, Integer, TIMESTAMP, Date, Numeric, Boolean, ForeignKey, text
 from sqlalchemy.dialects.postgresql import UUID
 from sqlalchemy.orm import Mapped, mapped_column, relationship
@@ -79,3 +80,4 @@ class ListItem(Base):
     sort_order: Mapped[int | None] = mapped_column(Integer)
 
     shopping_list: Mapped["ShoppingList"] = relationship("ShoppingList", back_populates="items")
+    product: Mapped[Optional["Product"]] = relationship("Product", lazy="select")