Commit design approval workflow and related features

- Add design approval workflow components and API routes
- Update checkout process for design approval integration
- Add admin navigation for design management
- Update mail utilities for design notifications
- Update types for design approval system
- Update Prisma schema for design approval database

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

src/app/checkout/client.tsx

@@ -133,6 +133,7 @@ export default function CheckoutPageClient({ isLoggedIn, customer }: CheckoutPag
                     }
 
                     console.log('📡 Fetching /api/checkout with', items.length, 'items');
+                    console.log('📦 Cart items:', JSON.stringify(items, null, 2));
                     const res = await fetch('/api/checkout', {
                       method: 'POST',
                       headers: { 'Content-Type': 'application/json' },