feat: show volume off icon when track volume is 0

- Volume icon now switches between Volume2 and VolumeX based on volume value
- Matches behavior of master volume controls for consistency
- Icon size remains consistent at h-3.5 w-3.5

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

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

components/tracks/Track.tsx

@@ -508,7 +508,11 @@ export function Track({
             {/* Volume */}
             <div className="flex items-center gap-2">
               <label className="text-xs text-muted-foreground flex items-center gap-1 w-16 flex-shrink-0">
-                <Volume2 className="h-3.5 w-3.5" />
+                {track.volume === 0 ? (
+                  <VolumeX className="h-3.5 w-3.5" />
+                ) : (
+                  <Volume2 className="h-3.5 w-3.5" />
+                )}
                 Volume
               </label>
               <div className="flex-1">