feat: streamline track and master controls layout consistency

- Streamlined track controls and master controls to same width (240px)
- Fixed track controls container to use full width of parent column
- Matched TrackControls card structure with MasterControls (gap-3, no w-full/h-full)
- Updated outer container padding from p-2 to p-4 with gap-4
- Adjusted track controls wrapper to center content instead of stretching
- Added max-width constraint to PlaybackControls to prevent width changes
- Centered transport control buttons in footer

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

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

components/editor/PlaybackControls.tsx

@@ -71,7 +71,7 @@ export function PlaybackControls({
   const progress = duration > 0 ? (currentTime / duration) * 100 : 0;
 
   return (
-    <div className={cn('space-y-4', className)}>
+    <div className={cn('space-y-4 w-full max-w-2xl', className)}>
       {/* Timeline Slider */}
       <div className="space-y-2">
         <input
@@ -161,7 +161,7 @@ export function PlaybackControls({
       )}
 
       {/* Transport Controls */}
-      <div className="flex items-center justify-between gap-4">
+      <div className="flex items-center justify-center gap-4">
         <div className="flex items-center gap-2">
           <Button
             variant="outline"