fix page settings section and blocks not showing in editor

Two bugs fixed:

1. Page Settings section wasn't appearing for system pages because
   Defaults.for_slug didn't return all required fields (type,
   meta_description, published, etc). Also changed page_renderer
   to use bracket notation for safer field access.

2. Blocks weren't loading when navigating directly to ?edit=page
   because the PageEditorHook's handle_params ran before Shop.Page
   assigned @page. Added pending page mode mechanism: hook sets a
   flag when edit mode is requested but @page is nil, then Shop.Page
   calls maybe_enter_pending_page_mode after @page is assigned.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/berrypod_web/components/shop_components/site_editor.ex

@@ -641,10 +641,8 @@ defmodule BerrypodWeb.ShopComponents.SiteEditor do
           class="site-editor-nav-item"
           data-item-id={item.id}
         >
-          <%
-            # Determine if this item links to a known page (by URL match or page_id)
-            is_page_link = item.page_id != nil or MapSet.member?(@page_urls, item.url)
-          %>
+          <% # Determine if this item links to a known page (by URL match or page_id)
+          is_page_link = item.page_id != nil or MapSet.member?(@page_urls, item.url) %>
           <form
             class="site-editor-nav-item-form"
             phx-change={@event_prefix <> "update_nav_item"}