Add customer accounts: login, signup, reset, activate, orders

- Storefront customer operations in graphql/customer.js and a server-safe
  services/shopify/customer.ts
- Session held in an httpOnly, sameSite=lax cookie set by the
  /api/account handlers; the access token never reaches client JS
- Pages: /account/login, /register, /recover, /reset/[id]/[token] and
  /activate/[id]/[token] for Shopify's emailed links
- /account renders order history as master-detail on one screen, since
  the Storefront API has no standalone order-by-id query for customers
- Header user icon: links to sign-in when signed out, otherwise a menu
  with name, email, order history, and sign out
- Login errors are collapsed and password recovery responds identically
  for known and unknown emails, so neither form enumerates accounts

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jWbNNJLksC1QG8z8845FX

app/api/account/me/route.ts

@@ -0,0 +1,19 @@
+import { getSessionToken } from '@/services/shopify/session';
+import { getCustomer } from '@/services/shopify/customer';
+
+// Minimal session probe for the header menu — never returns the access token.
+export async function GET() {
+  const token = await getSessionToken();
+  if (!token) return Response.json({ customer: null });
+
+  const customer = await getCustomer(token, 0);
+  if (!customer) return Response.json({ customer: null });
+
+  return Response.json({
+    customer: {
+      displayName: customer.displayName,
+      email: customer.email,
+      firstName: customer.firstName,
+    },
+  });
+}