fix: add missing cn import to TrackList

- Import cn utility function from @/lib/utils/cn
- Fixes ReferenceError: cn is not defined
- Required for conditional classNames on effect labels

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

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

components/tracks/TrackList.tsx

@@ -3,6 +3,7 @@
 import * as React from 'react';
 import { Plus, Upload, ChevronDown, ChevronRight, X, Eye, EyeOff } from 'lucide-react';
 import { Button } from '@/components/ui/Button';
+import { cn } from '@/lib/utils/cn';
 import { Track } from './Track';
 import { TrackExtensions } from './TrackExtensions';
 import { ImportTrackDialog } from './ImportTrackDialog';