Replace shared _added.html with market-owned version using cart-mini fragment

The shared _added.html imported _types/cart/_cart.html which only
exists in the cart app. Market now has its own _added.html that:
- Fetches cart-mini fragment for the OOB mini cart update
- Uses market's own _types/product/_cart.html macros
- Drops cart summary/show_cart (not visible on product pages)

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

templates/_types/product/_added.html

@@ -0,0 +1,16 @@
+{# HTMX response after add-to-cart: OOB-swap the mini cart + product buttons #}
+{% import '_types/product/_cart.html' as _cart %}
+
+{# 1. Update mini cart via cart-mini fragment #}
+{{ cart_mini_html | safe }}
+
+{# 2. Update add/remove buttons on the product #}
+{{ _cart.add(d.slug, cart, oob='true') }}
+
+{# 3. Update cart item row if visible #}
+{% from '_types/product/_cart.html' import cart_item with context %}
+{% if item and item.quantity > 0 %}
+  {{ cart_item(oob='true') }}
+{% elif item %}
+  {{ cart_item(oob='delete') }}
+{% endif %}