Pass product data to cart _added.html template

resolve_product skips for POST so g.item_data (and thus d) is not
set. Pass d={slug} directly in the render_template call.

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

bp/product/routes.py

@@ -265,6 +265,7 @@ def register():
 
             return await render_template(
                 "_types/product/_added.html",
+                d={"slug": slug},
                 cart=g.cart,
                 item=ci,
                 total=total,