fix PDP quantity selector and trust badge consistency

Wire up +/− buttons with phx-click events and handle_event handlers,
clamp to 1–99, reset to 1 after add-to-cart. Trust badges now use a
single hero-check-circle icon and sentence case text.

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

lib/simpleshop_theme_web/live/shop_live/product_show.ex

@@ -130,6 +130,18 @@ defmodule SimpleshopThemeWeb.ShopLive.ProductShow do
     {:noreply, socket}
   end
 
+  @impl true
+  def handle_event("increment_quantity", _params, socket) do
+    quantity = min(socket.assigns.quantity + 1, 99)
+    {:noreply, assign(socket, :quantity, quantity)}
+  end
+
+  @impl true
+  def handle_event("decrement_quantity", _params, socket) do
+    quantity = max(socket.assigns.quantity - 1, 1)
+    {:noreply, assign(socket, :quantity, quantity)}
+  end
+
   @impl true
   def handle_event("add_to_cart", _params, socket) do
     variant = socket.assigns.selected_variant
@@ -140,6 +152,7 @@ defmodule SimpleshopThemeWeb.ShopLive.ProductShow do
       socket =
         socket
         |> SimpleshopThemeWeb.CartHook.broadcast_and_update(cart)
+        |> assign(:quantity, 1)
         |> assign(:cart_drawer_open, true)
         |> assign(:cart_status, "#{socket.assigns.product.name} added to cart")