Major refactor to simplify the editor and focus exclusively on multi-track editing:
**AudioEditor Changes:**
- Removed single-file waveform view and useAudioPlayer
- Removed all single-file editing operations (cut, copy, paste, trim)
- Simplified to multi-track only with track selection support
- Added selectedTrackId state for track-specific effect chain
- Reduced from ~1500 lines to ~290 lines
**SidePanel Changes:**
- Complete rewrite with 2 tabs: Tracks and Effect Chain
- Tracks tab shows all tracks with inline controls (volume, pan, solo, mute)
- Click tracks to select/deselect
- Effect Chain tab shows effects for selected track
- Removed old file/history/info/effects tabs
- Sidebar now wider (320px) to accommodate inline track controls
**TrackList/Track Changes:**
- Added track selection support (isSelected/onSelect props)
- Visual feedback with ring border when track is selected
- Click anywhere on track to select it
**Workflow:**
1. Import or add audio tracks
2. Select a track in the sidebar or main view
3. Apply effects to selected track via Effect Chain tab
4. Adjust track controls (volume, pan, solo, mute) in Tracks tab
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Co-Authored-By: Claude <noreply@anthropic.com>