extract site_name and site_description from theme settings into standalone settings

site_name and site_description are shop identity, not theme concerns.
They now live in the Settings table as first-class settings with their
own assigns (@site_name, @site_description) piped through hooks and
plugs. The setup wizard writes site_name on account creation, and the
theme editor reads/writes via Settings.put_setting. Removed the
"configure your shop" checklist item since currency/country aren't
built yet. Also adds shop name field to setup wizard step 1.

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

lib/berrypod_web/live/admin/pages/editor.ex

@@ -688,6 +688,7 @@ defmodule BerrypodWeb.Admin.Pages.Editor do
             page_data={@page_data}
             preview_data={@preview_data}
             theme_settings={@theme_settings}
+            site_name={@site_name}
             generated_css={@generated_css}
             logo_image={@logo_image}
             header_image={@header_image}