Fix undefined calendar_total/calendar_cart_entries in product cart template

The _added.html template's summary macro expects calendar_total and
calendar_cart_entries from the cart/events domain. The market app has
no calendar entries, so pass a no-op function and empty list.

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

bp/product/routes.py

@@ -250,7 +250,9 @@ def register():
                 "_types/product/_added.html",
                 cart=g.cart,
                 item=ci,
-                total = total
+                total=total,
+                calendar_total=lambda entries: 0,
+                calendar_cart_entries=[],
             )
 
         # normal POST: go to cart page