🔧 Fix Thumbnails API Result Structure

🐛 Bug Fix:
- Fixed thumbnailsResult.map() error in thumbnails API
- Added null safety with (thumbnailsResult || [])
- Updated response to wrap thumbnails in object: { thumbnails }

✅ Expected Results:
- Thumbnails API should now work without errors
- Collections should display proper thumbnail layouts:
  😢 Empty collections → crying emoji
  🃏 Collections with cards → white card boxes
  🖼️ Custom thumbnails → uploaded images

The new thumbnail layouts should now display correctly! 🎨

pages/api/collections/[identifier]/thumbnails.js

@@ -114,7 +114,7 @@ export default async function handler(req, res) {
       LIMIT 5
     `;
 
-    const thumbnails = thumbnailsResult.map(card => ({
+    const thumbnails = (thumbnailsResult || []).map(card => ({
       id: card.id,
       name: card.name,
       rarity: card.rarity,
@@ -126,7 +126,7 @@ export default async function handler(req, res) {
       quantity: parseInt(card.quantity) || 1
     }));
 
-    res.status(200).json(thumbnails);
+    res.status(200).json({ thumbnails });
 
   } catch (error) {
     console.error('Error fetching collection thumbnails:', error);