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/live/admin/email_settings.ex

@@ -27,9 +27,15 @@ defmodule BerrypodWeb.Admin.EmailSettings do
        Settings.get_setting("email_from_address") || socket.assigns.current_scope.user.email
      )
      |> assign(:sending_test, false)
+     |> assign(:from_checklist, false)
      |> assign(:form, to_form(%{}, as: :email))}
   end
 
+  @impl true
+  def handle_params(params, _uri, socket) do
+    {:noreply, assign(socket, :from_checklist, params["from"] == "checklist")}
+  end
+
   defp load_adapter_values(adapter_key) do
     case Adapters.get(adapter_key) do
       nil ->
@@ -201,6 +207,15 @@ defmodule BerrypodWeb.Admin.EmailSettings do
   def render(assigns) do
     ~H"""
     <div class="admin-content-medium">
+      <div :if={@from_checklist} class="admin-checklist-banner">
+        <.icon name="hero-clipboard-document-check" class="size-5 admin-checklist-banner-icon" />
+        <span class="admin-checklist-banner-text">
+          You're setting up email for your shop.
+        </span>
+        <.link navigate={~p"/admin"} class="admin-link admin-checklist-banner-link">
+          &larr; Back to checklist
+        </.link>
+      </div>
       <.header>
         Email settings
         <:subtitle>