feat: add border styling to TrackControls to match MasterControls

Added consistent border styling:
- bg-muted/10 background
- border-2 border-accent/30
- rounded-lg corners
- px-3 horizontal padding

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

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

components/tracks/TrackControls.tsx

@@ -56,7 +56,10 @@ export function TrackControls({
   className,
 }: TrackControlsProps) {
   return (
-    <div className={cn('flex flex-col items-center justify-between h-full py-2', className)}>
+    <div className={cn(
+      'flex flex-col items-center justify-between h-full px-3 py-2 bg-muted/10 border-2 border-accent/30 rounded-lg',
+      className
+    )}>
       {/* Pan Control - Top */}
       <div className="flex justify-center w-full">
         <CircularKnob