improve setup UX: password field, setup hook, checklist banners, theme tweaks

- add password field and required shop name to setup wizard
- extract SetupHook for DRY redirect to /setup when no admin exists
- add ?from=checklist param to checklist hrefs with contextual banner on
  email settings and theme pages for easy return to dashboard
- remove email warning banner from admin layout (checklist covers it)
- make email a required checklist item (no longer optional)
- add DevReset module for wiping dev data without restart
- rename "Theme Studio" to "Theme", drop subtitle
- lower theme editor side-by-side breakpoint from 64em to 48em
- clean up login/registration pages (remove dead registration_open code)
- fix settings.put_secret to invalidate cache after write

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

test/berrypod_web/live/shop/coming_soon_test.exs

@@ -17,6 +17,7 @@ defmodule BerrypodWeb.Shop.ComingSoonTest do
     end
 
     test "displays the shop name", %{conn: conn} do
+      user_fixture()
       Settings.put_setting("site_name", "My Test Shop", "string")
 
       {:ok, _view, html} = live(conn, ~p"/coming-soon")