add contextual prompts for skipped setup steps

Disable checkout when Stripe isn't connected (cart drawer, cart page,
and early guard in checkout controller to prevent orphaned orders).
Show amber warning on order detail when email isn't configured.
Fix pre-existing missing vertical spacing between page blocks.

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

lib/berrypod_web/controllers/checkout_controller.ex

@@ -1,23 +1,29 @@
 defmodule BerrypodWeb.CheckoutController do
   use BerrypodWeb, :controller
 
-  alias Berrypod.{Analytics, Cart}
+  alias Berrypod.{Analytics, Cart, Settings}
   alias Berrypod.Orders
   alias Berrypod.Shipping
 
   require Logger
 
   def create(conn, _params) do
-    cart_items = Cart.get_from_session(get_session(conn))
-    hydrated = Cart.hydrate(cart_items)
-
-    if hydrated == [] do
+    unless Settings.has_secret?("stripe_api_key") do
       conn
-      |> put_flash(:error, "Your basket is empty")
+      |> put_flash(:error, "Checkout isn't available yet")
       |> redirect(to: ~p"/cart")
     else
-      track_checkout_start(conn)
-      create_checkout(conn, hydrated)
+      cart_items = Cart.get_from_session(get_session(conn))
+      hydrated = Cart.hydrate(cart_items)
+
+      if hydrated == [] do
+        conn
+        |> put_flash(:error, "Your basket is empty")
+        |> redirect(to: ~p"/cart")
+      else
+        track_checkout_start(conn)
+        create_checkout(conn, hydrated)
+      end
     end
   end