Fix events: use cart-mini fragment instead of local cart template

Events was trying to render _types/cart/_mini.html locally, which only
exists in the cart service. Replace with fetch_fragment("cart", "cart-mini")
calls and add oob param support to the cart-mini fragment.

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

cart/templates/fragments/cart_mini.html

@@ -1,4 +1,4 @@
-<div id="cart-mini">
+<div id="cart-mini" {% if oob %}hx-swap-oob="true"{% endif %}>
   {% if cart_count == 0 %}
   <div class="h-12 w-12 rounded-full overflow-hidden border border-stone-300 flex-shrink-0">
     <a