Fix cart quantities not showing on product list after page refresh

The context processor loaded cart items but only passed aggregates
(cart_count, cart_total) — not the cart list itself. Templates need
the full list to display per-product quantities.

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

app.py

@@ -46,6 +46,7 @@ async def market_context() -> dict:
     cart_items = cart_result.scalars().all()
 
     from bp.cart.services import total
+    ctx["cart"] = list(cart_items)
     ctx["cart_count"] = sum(ci.quantity for ci in cart_items)
     ctx["cart_total"] = total(cart_items) or 0