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/controllers/favicon_controller.ex

@@ -25,15 +25,16 @@ defmodule BerrypodWeb.FaviconController do
 
   def webmanifest(conn, _params) do
     settings = Settings.get_theme_settings()
+    site_name = Settings.site_name()
 
     short_name =
       case settings.favicon_short_name do
         name when is_binary(name) and name != "" -> name
-        _ -> String.slice(settings.site_name, 0, 12)
+        _ -> String.slice(site_name, 0, 12)
       end
 
     manifest = %{
-      name: settings.site_name,
+      name: site_name,
       short_name: short_name,
       theme_color: settings.accent_color || "#000000",
       background_color: settings.icon_background_color || "#ffffff",