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>

lib/berrypod_web/theme_hook.ex

@@ -82,10 +82,6 @@ defmodule BerrypodWeb.ThemeHook do
       socket.assigns[:current_scope] && socket.assigns.current_scope.user ->
         {:cont, socket}
 
-      not Berrypod.Accounts.has_admin?() ->
-        # Fresh install — send to setup
-        {:halt, Phoenix.LiveView.redirect(socket, to: "/setup")}
-
       true ->
         {:halt, Phoenix.LiveView.redirect(socket, to: "/coming-soon")}
     end