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/register/route.ts

@@ -0,0 +1,39 @@
+import {
+  createCustomer,
+  login,
+  customerErrorMessage,
+} from '@/services/shopify/customer';
+import { setSessionToken } from '@/services/shopify/session';
+
+export async function POST(req: Request) {
+  const { email, password, firstName, lastName } = await req.json();
+
+  if (!email || !password) {
+    return Response.json(
+      { error: 'Enter your email and password.' },
+      { status: 400 }
+    );
+  }
+
+  const { errors } = await createCustomer({
+    email,
+    password,
+    firstName,
+    lastName,
+  });
+
+  if (errors.length) {
+    return Response.json({ error: customerErrorMessage(errors) }, { status: 400 });
+  }
+
+  // Sign the new customer straight in. Accounts needing email confirmation
+  // won't return a token yet, which is not an error.
+  const { token } = await login(email, password);
+
+  if (token) {
+    await setSessionToken(token.accessToken, token.expiresAt);
+    return Response.json({ ok: true, signedIn: true });
+  }
+
+  return Response.json({ ok: true, signedIn: false });
+}