Fix price display issues and layout in design review page

- Add defensive checks in cart store to handle missing/NaN unitPrice values
- Display '—' for items with invalid prices instead of NaN
- Fix design review page grid layout to align buttons at top of page
- Ensure buttons don't get pushed below images on review page

src/lib/cartStore.ts

@@ -38,7 +38,10 @@ export const useCart = create<CartState>()(
           ),
         })),
       clear: () => set({ items: [] }),
-      total: () => get().items.reduce((sum, i) => sum + i.unitPrice * i.quantity, 0),
+      total: () => get().items.reduce((sum, i) => {
+        const price = typeof i.unitPrice === 'number' && !isNaN(i.unitPrice) ? i.unitPrice : 0;
+        return sum + price * i.quantity;
+      }, 0),
     }),
     {
       name: 'personalize-studio-cart',