Add admin menu link to header when authenticated

- Check isAdminAuthenticated() in Header component
- Show 'Admin' link to /admin/orders when user is logged in as admin
- Allows quick navigation to admin section after login

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/components/Header.tsx

@@ -8,15 +8,17 @@ import CurrencySelector from './CurrencySelector';
 import MobileNav from './MobileNav';
 import { prisma } from '@/lib/prisma';
 import { getCurrentCustomer } from '@/lib/auth';
+import { isAdminAuthenticated } from '@/lib/adminAuth';
 
 export default async function Header() {
-  const [categories, collections, customer] = await Promise.all([
+  const [categories, collections, customer, isAdmin] = await Promise.all([
     prisma.category.findMany({
       where: { showOnPersonalised: true },
       orderBy: { name: 'asc' },
     }),
     prisma.collection.findMany({ orderBy: { name: 'asc' } }),
     getCurrentCustomer(),
+    isAdminAuthenticated(),
   ]);
   const personalisedLinks = [
     { href: '/made-to-order', label: 'Shop all' },
@@ -69,6 +71,11 @@ export default async function Header() {
         </nav>
         <div className="flex items-center gap-2 sm:gap-4">
           <CurrencySelector />
+          {isAdmin && (
+            <Link href="/admin/orders" className="tag-label hover:text-ink">
+              Admin
+            </Link>
+          )}
           <div className="hidden md:block">
             <AccountMenu customer={customer ? { name: customer.name, email: customer.email } : null} />
           </div>