fix: resolve TypeScript syntax error in music routes - use spread operator instead of invalid 'as string[]' syntax

packages/backend/src/routes/music.ts

@@ -227,7 +227,7 @@ router.get('/folders', async (req, res) => {
   try {
     const folders = await s3Service.listAllFolders('');
     // Include root option as empty string
-    res.json({ folders: [''] as string[] .concat(folders) });
+    res.json({ folders: ['', ...folders] });
   } catch (error) {
     console.error('Error fetching S3 folders:', error);
     res.status(500).json({ error: 'Failed to fetch S3 folders' });