Fix AttributeError on g.cart in product cart route

g.cart was never populated in the market app — the cart loader
before_request hook was only registered in the cart microservice.
Replace the dead filter-building code with an actual query that
loads cart items inline, scoped to the current user/session.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

bp/product/routes.py

@@ -192,11 +192,23 @@ def register():
 
         ident = current_cart_identity()
 
-        filters = [CartItem.deleted_at.is_(None), CartItem.product_id == product_id]
+        # Load cart items for current user/session
+        from sqlalchemy.orm import selectinload
+        cart_filters = [CartItem.deleted_at.is_(None)]
         if ident["user_id"] is not None:
-            filters.append(CartItem.user_id == ident["user_id"])
+            cart_filters.append(CartItem.user_id == ident["user_id"])
         else:
-            filters.append(CartItem.session_id == ident["session_id"])
+            cart_filters.append(CartItem.session_id == ident["session_id"])
+        cart_result = await g.s.execute(
+            select(CartItem)
+            .where(*cart_filters)
+            .order_by(CartItem.created_at.desc())
+            .options(
+                selectinload(CartItem.product),
+                selectinload(CartItem.market_place),
+            )
+        )
+        g.cart = list(cart_result.scalars().all())
 
         ci = next(
             (item for item in g.cart if item.product_id == product_id),