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>

bp/product/routes.py

@@ -252,19 +252,23 @@ def register():
 
         # no explicit commit; your session middleware should handle it
 
-        # htmx support (optional)
+        # htmx response: OOB-swap mini cart + product buttons
         if request.headers.get("HX-Request") == "true":
-            # You can return a small fragment or mini-cart here
+            from shared.infrastructure.fragments import fetch_fragment
+            from shared.infrastructure.cart_identity import current_cart_identity as _ci
+            frag_ident = _ci()
+            cart_params = {}
+            if frag_ident["user_id"] is not None:
+                cart_params["user_id"] = frag_ident["user_id"]
+            if frag_ident["session_id"] is not None:
+                cart_params["session_id"] = frag_ident["session_id"]
+            cart_mini_html = await fetch_fragment("cart", "cart-mini", params=cart_params)
 
             return await render_template(
                 "_types/product/_added.html",
+                cart_mini_html=cart_mini_html,
                 cart=g.cart,
                 item=ci,
-                total=total,
-                cart_count=sum(i.quantity for i in g.cart),
-                cart_total=total(g.cart),
-                calendar_total=lambda entries: 0,
-                calendar_cart_entries=[],
             )
 
         # normal POST: go to cart page