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>

test/berrypod_web/live/setup/onboarding_test.exs

@@ -10,7 +10,7 @@ defmodule BerrypodWeb.Setup.OnboardingTest do
     test "accessible on fresh install (no admin)", %{conn: conn} do
       {:ok, _view, html} = live(conn, ~p"/setup")
       assert html =~ "Set up your shop"
-      assert html =~ "Create admin account"
+      assert html =~ "Set up your account"
     end
 
     test "redirects to /admin when setup is complete", %{conn: conn} do
@@ -60,7 +60,7 @@ defmodule BerrypodWeb.Setup.OnboardingTest do
     test "shows all three cards with email form active", %{conn: conn} do
       {:ok, _view, html} = live(conn, ~p"/setup")
 
-      assert html =~ "Create admin account"
+      assert html =~ "Set up your account"
       assert html =~ "Connect a print provider"
       assert html =~ "Connect payments"
     end
@@ -114,7 +114,7 @@ defmodule BerrypodWeb.Setup.OnboardingTest do
       {:ok, _view, html} = live(conn, ~p"/setup")
 
       assert html =~ "Secret key"
-      assert html =~ "Connect Stripe"
+      assert html =~ "Connect payments"
     end
   end