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/router.ex

@@ -192,7 +192,10 @@ defmodule BerrypodWeb.Router do
     pipe_through [:browser]
 
     live_session :current_user,
-      on_mount: [{BerrypodWeb.UserAuth, :mount_current_scope}] do
+      on_mount: [
+        {BerrypodWeb.SetupHook, :require_admin},
+        {BerrypodWeb.UserAuth, :mount_current_scope}
+      ] do
       live "/users/register", Auth.Registration, :new
       live "/users/log-in", Auth.Login, :new
       live "/users/log-in/:token", Auth.Confirmation, :new
@@ -239,6 +242,7 @@ defmodule BerrypodWeb.Router do
     live_session :coming_soon,
       layout: {BerrypodWeb.Layouts, :shop},
       on_mount: [
+        {BerrypodWeb.SetupHook, :require_admin},
         {BerrypodWeb.ThemeHook, :mount_theme}
       ] do
       live "/coming-soon", Shop.ComingSoon, :index
@@ -247,6 +251,7 @@ defmodule BerrypodWeb.Router do
     live_session :public_shop,
       layout: {BerrypodWeb.Layouts, :shop},
       on_mount: [
+        {BerrypodWeb.SetupHook, :require_admin},
         {BerrypodWeb.UserAuth, :mount_current_scope},
         {BerrypodWeb.ThemeHook, :mount_theme},
         {BerrypodWeb.ThemeHook, :require_site_live},