Improve debug logging for checkout flow

Add emoji-prefixed logs to make debugging easier:
- 💳 Checkout button clicked
- ✓ Flag set/skipped actions
- 🚪 LogoutOnUnload handler
- 📡 API fetch
- 📦 API response
- 🔗 Stripe redirect
- 🗑️ Cart clearing

This makes it much easier to see the flow in the console.

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

src/components/LogoutOnUnload.tsx

@@ -10,20 +10,21 @@ import { useCart } from '@/lib/cartStore';
  */
 export default function LogoutOnUnload() {
   const clearCart = useCart((s) => s.clear);
+  const cartItems = useCart((s) => s.items);
 
   useEffect(() => {
     const handleUnload = () => {
       // Don't logout if we're in the middle of checkout (navigating to Stripe)
       // The checkout component sets this flag before making the API call
       const isCheckingOut = typeof window !== 'undefined' && sessionStorage.getItem('isCheckingOut');
-      console.log('LogoutOnUnload handleUnload called, isCheckingOut flag:', isCheckingOut);
+      console.log('🚪 LogoutOnUnload handleUnload - cart items:', cartItems.length, 'isCheckingOut:', isCheckingOut);
       if (isCheckingOut) {
-        console.log('Skipping logout because isCheckingOut is set');
+        console.log('✓ Skipping logout - checkout in progress');
         return;
       }
 
       // Clear cart on logout
-      console.log('Clearing cart and logging out');
+      console.log('🗑️ Clearing cart and logging out');
       clearCart();
       // Use sendBeacon to reliably send logout even when page is closing
       // This doesn't wait for a response, which is fine for logout