fix search modal closing on keypress and add admin header icon

Track search_open as server state so morphdom doesn't reset display
to none on re-render. Move admin bar from layout banner to a gear
icon in the header actions. Extract layout_assigns/1 helper so page
templates use a spread instead of listing every attr explicitly.

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

lib/simpleshop_theme_web/live/shop/collection.ex

@@ -81,20 +81,7 @@ defmodule SimpleshopThemeWeb.Shop.Collection do
   @impl true
   def render(assigns) do
     ~H"""
-    <.shop_layout
-      theme_settings={@theme_settings}
-      logo_image={@logo_image}
-      header_image={@header_image}
-      mode={@mode}
-      cart_items={@cart_items}
-      cart_count={@cart_count}
-      cart_subtotal={@cart_subtotal}
-      cart_drawer_open={@cart_drawer_open}
-      cart_status={assigns[:cart_status]}
-      active_page="collection"
-      search_query={assigns[:search_query] || ""}
-      search_results={assigns[:search_results] || []}
-    >
+    <.shop_layout {layout_assigns(assigns)} active_page="collection">
       <main id="main-content">
         <.collection_header
           title={@collection_title}