Fix: Safely parse designJson in admin order detail page

The order detail page was trying to access design.front.length and
design.back.length without safely checking if they exist. Now wraps
the parse in try-catch and uses optional chaining to handle errors
gracefully.

src/app/admin/orders/[id]/page.tsx

@@ -78,9 +78,15 @@ export default async function OrderDetailPage({ params }: { params: { id: string
 
       <div className="mt-10 divide-y divide-line border-t border-line">
         {order.items.map((item) => {
-          const design = JSON.parse(item.designJson) as { front: unknown[]; back: unknown[] };
-          const hasFrontDesign = design.front.length > 0;
-          const hasBackDesign = design.back.length > 0;
+          let hasFrontDesign = false;
+          let hasBackDesign = false;
+          try {
+            const design = JSON.parse(item.designJson) as { front: unknown[]; back: unknown[] };
+            hasFrontDesign = (design.front?.length ?? 0) > 0;
+            hasBackDesign = (design.back?.length ?? 0) > 0;
+          } catch {
+            // If parsing fails, assume no custom design
+          }
           const frontPlacement = item.placementPreviewUrl || item.designPreviewUrl;
           return (
             <div key={item.id} className="py-8">