fix: increase default track height to accommodate input meter

Increased DEFAULT_TRACK_HEIGHT from 120px to 150px to properly fit:
- Volume slider
- Pan slider
- Input level meter (when track is armed or recording)

This ensures all controls have adequate vertical spacing and the input
meter doesn't get cramped when it appears under the pan control.

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

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

types/track.ts

@@ -59,6 +59,6 @@ export const TRACK_COLORS: Record<TrackColor, string> = {
   gray: 'rgb(156, 163, 175)',
 };
 
-export const DEFAULT_TRACK_HEIGHT = 120;
+export const DEFAULT_TRACK_HEIGHT = 150;
 export const MIN_TRACK_HEIGHT = 60;
 export const MAX_TRACK_HEIGHT = 300;