docs(timeline-editor): Document WAV source and music.track visualization task

Updated documentation:

README.md:
- Added waveform visualization to implemented features list
- Added section on loading audio waveform with usage instructions
- Documented wav_dump_backend integration: ./demo64k --dump_wav output.wav
- Added snap-to-beat and resize handles to feature list
- Updated Future Enhancements with music.track visualization

ROADMAP.md:
- Added Phase 2.5: Music.track Visualization & Overlay
- Detailed implementation plan for tracker score overlay
- Visual design specifications (colored bars, sample markers)
- Use case: Align visual sequences with tracker events
- Effort: 12-15 hours, Priority: MEDIUM

The timeline editor now has clear guidance on:
1. How to generate WAV files from demo64k for visual reference
2. Future feature: Display tracker patterns/samples for alignment

1 files changed, 25 insertions, 4 deletions

diff --git a/tools/timeline_editor/README.md b/tools/timeline_editor/README.md
index 1c73c53..adf9d4e 100644
--- a/tools/timeline_editor/README.md
+++ b/tools/timeline_editor/README.md
@@ -9,13 +9,16 @@ Interactive web-based editor for `demo.seq` timeline files.
 - 📊 Visual Gantt-style timeline
 - 🎯 Drag & drop sequences along timeline
 - 🎯 Drag & drop effects along timeline
+- 🎯 Resize effects with left/right handles
 - ⏱️ Edit timing (start/end times)
-- ⚙️ Edit priorities
+- ⚙️ Stack-order based priority system
 - ⚙️ Edit effect class names and constructor arguments
 - 🔍 Zoom in/out (10% - 200%)
+- 🎵 Audio waveform visualization (WAV files)
 - 📋 Real-time statistics
 - 🗑️ Delete sequences/effects
 - ➕ Add new sequences
+- 🎼 Snap-to-beat mode with beat markers
 
 ## Usage
 
@@ -39,9 +42,27 @@ Interactive web-based editor for `demo.seq` timeline files.
    - Click "💾 Save demo.seq"
    - Choose where to save the modified file
 
-5. **Zoom controls:**
+5. **Load audio waveform (optional):**
+   - Click "🎵 Load Audio (WAV)" to visualize your music track
+   - The waveform appears above the timeline for visual reference
+   - Use it to align sequences with beats, drops, and musical phrases
+   - Click "✖ Clear Audio" to remove the waveform
+
+   **Tip:** Generate a WAV file from your demo using:
+   ```bash
+   ./build/demo64k --dump_wav output.wav
+   ```
+   Then load `output.wav` in the timeline editor to align sequences with the actual audio output.
+
+6. **Zoom controls:**
    - Use the zoom slider to adjust timeline scale
    - Higher zoom = more pixels per second
+   - Waveform scales automatically with zoom
+
+7. **Snap-to-beat mode:**
+   - Enable "Show Beats" checkbox to display beat markers
+   - Sequences and effects snap to beat boundaries when dragged
+   - Helps maintain musical timing
 
 ## Keyboard Shortcuts
 
@@ -109,12 +130,12 @@ SEQUENCE 4b 1 "Beat Drop"
 ## Future Enhancements
 
 - [ ] Undo/redo functionality
-- [ ] Add effect button
+- [ ] Add effect button (create new effects within sequences)
 - [ ] Overlap detection warnings
-- [ ] Snap-to-grid
 - [ ] Timeline playback indicator
 - [ ] Multiple file comparison
 - [ ] Export to different formats
+- [ ] **Music.track visualization**: Parse `music.track` file and overlay tracker patterns/samples on timeline for alignment assistance
 
 ## Technical Details