fix: convert track name to string to prevent React error

Added String() conversion to track.name display to ensure it's always rendered as text, preventing "Objects are not valid as a React child" error.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

components/layout/SidePanel.tsx

@@ -188,7 +188,7 @@ export function SidePanel({
                         <div className="flex items-center justify-between mb-2">
                           <div className="flex-1 min-w-0">
                             <div className="text-sm font-medium text-foreground truncate">
-                              {track.name}
+                              {String(track.name || 'Untitled Track')}
                             </div>
                             {track.audioBuffer && (
                               <div className="text-xs text-muted-foreground">