add setup foundations: site gate, registration lockdown, coming soon page

- Settings.site_live?/0 and set_site_live/1 for shop visibility control
- Accounts.has_admin?/0 to detect single-tenant admin existence
- Registration lockdown: /users/register redirects when admin exists
- Setup.setup_status/0 aggregates provider, product, and stripe checks
- Coming soon page at /coming-soon with themed styling
- ThemeHook :require_site_live gate on all public shop routes
  - Site live → everyone through
  - Authenticated → admin preview through
  - No admin → fresh install demo through
  - Otherwise → redirect to coming soon
- Go live / take offline toggle on /admin/settings
- 648 tests, 0 failures

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

lib/simpleshop_theme/accounts.ex

@@ -60,6 +60,15 @@ defmodule SimpleshopTheme.Accounts do
   """
   def get_user!(id), do: Repo.get!(User, id)
 
+  @doc """
+  Returns whether an admin user exists.
+
+  SimpleShop is single-tenant — any user in the database is the admin.
+  """
+  def has_admin? do
+    Repo.exists?(User)
+  end
+
   ## User registration
 
   @doc """

lib/simpleshop_theme/settings.ex

@@ -116,6 +116,22 @@ defmodule SimpleshopTheme.Settings do
     end
   end
 
+  @doc """
+  Returns whether the shop is live (visible to the public).
+
+  Defaults to `false` for fresh installs.
+  """
+  def site_live? do
+    get_setting("site_live", false) == true
+  end
+
+  @doc """
+  Sets whether the shop is live (visible to the public).
+  """
+  def set_site_live(live?) when is_boolean(live?) do
+    put_setting("site_live", live?, "boolean")
+  end
+
   @doc """
   Deletes a setting by key.
   """

lib/simpleshop_theme/setup.ex

@@ -0,0 +1,33 @@
+defmodule SimpleshopTheme.Setup do
+  @moduledoc """
+  Aggregates setup status checks for the admin setup flow.
+  """
+
+  alias SimpleshopTheme.{Accounts, Products, Settings}
+
+  @doc """
+  Returns a map describing the current setup status.
+
+  Used by the admin setup checklist and ThemeHook gate to determine
+  what's been completed and whether the shop can go live.
+  """
+  def setup_status do
+    conn = Products.get_provider_connection_by_type("printify")
+    product_count = Products.count_products_for_connection(conn && conn.id)
+
+    printify_connected = conn != nil and conn.api_key_encrypted != nil
+    products_synced = product_count > 0
+    stripe_connected = Settings.has_secret?("stripe_api_key")
+    site_live = Settings.site_live?()
+
+    %{
+      admin_created: Accounts.has_admin?(),
+      printify_connected: printify_connected,
+      products_synced: products_synced,
+      product_count: product_count,
+      stripe_connected: stripe_connected,
+      site_live: site_live,
+      can_go_live: printify_connected and products_synced and stripe_connected
+    }
+  end
+end