Add real order persistence, customer accounts, and cart sync

Checkout now persists orders server-side (Payload orders collection,
re-priced from live product data, discount codes redeemed exactly once)
instead of writing a client-only sessionStorage snapshot. Buying requires
an account (registration inline in checkout, no separate step) — accounts
get order history with delivery status, profile/address editing, password
change, and a cart that syncs across devices while logged in.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/checkout/page.tsx

@@ -3,6 +3,7 @@ import { CheckoutContent } from "./components/CheckoutContent";
 import { TrustRow } from "../components/TrustRow";
 import { Footer } from "../components/Footer";
 import { getShippingMethods, getPaymentMethods, getCartTrustBadges, getShippingSettings } from "../lib/payload";
+import { getSessionCustomer, getCustomerProfile } from "../lib/customerAuth";
 
 // robots: noindex — transactional page, same reasoning as /cart.
 export const metadata: Metadata = {
@@ -15,12 +16,16 @@ export const metadata: Metadata = {
 };
 
 export default async function CheckoutPage() {
-  const [shippingMethods, paymentMethods, trustBadges, shippingSettings] = await Promise.all([
+  const [shippingMethods, paymentMethods, trustBadges, shippingSettings, session] = await Promise.all([
     getShippingMethods(),
     getPaymentMethods(),
     getCartTrustBadges(),
     getShippingSettings(),
+    getSessionCustomer(),
   ]);
+  // Full profile (incl. saved address) only fetched when a session exists
+  // — pre-fills Card 1 for a returning customer instead of leaving it blank.
+  const profile = session ? await getCustomerProfile(session.token) : null;
 
   return (
     <>
@@ -30,6 +35,8 @@ export default async function CheckoutPage() {
           paymentMethods={paymentMethods}
           trustBadges={trustBadges}
           shippingSettings={shippingSettings}
+          customerEmail={session?.customer.email ?? null}
+          savedProfile={profile}
         />
         <TrustRow />
       </main>