docs(04-01): complete timeline canvas foundation plan — SUMMARY, STATE, ROADMAP updated

- SUMMARY: timeline canvas with per-device tracks, waveform, beat marks, playback cursor
- STATE: plan advanced to 2/4, progress 79%, decisions and metrics recorded
- ROADMAP: Phase 4 progress updated (1/4 plans complete, In Progress)
- Requirements TL-01, TL-05 marked complete

.planning/ROADMAP.md

@@ -90,7 +90,7 @@ Plans:
 **Plans**: 4 plans
 
 Plans:
-- [ ] 04-01: Timeline canvas — per-device tracks, time axis, block rendering, playback cursor
+- [x] 04-01: Timeline canvas — per-device tracks, time axis, block rendering, playback cursor
 - [ ] 04-02: Block interactions — drag-and-place, move, resize, delete; command pattern undo/redo (min 20 steps)
 - [ ] 04-03: Beat detection + snap — librosa beat_track + plp + onset_detect in ProcessPoolExecutor, beat mark overlay, snap-to-beat, calibration offset UI
 - [ ] 04-04: Block editor — animation library panel, color picker, parameter controls per block, changes reflected in show file
@@ -155,7 +155,7 @@ Phases execute in numeric order: 1 → 2 → 3 → 4 → 5 → 6 → 7
 | 1. Foundation | 4/4 | Complete   | 2026-04-05 |
 | 2. Audio Engine | 3/3 | Complete   | 2026-04-06 |
 | 3. Communication Protocol | 3/3 | Complete   | 2026-04-06 |
-| 4. Timeline Editor | 0/4 | Not started | - |
+| 4. Timeline Editor | 1/4 | In Progress|  |
 | 5. Live Show Execution | 0/3 | Not started | - |
 | 6. AI Sync | 0/3 | Not started | - |
 | 7. Microcontroller Firmware | 0/3 | Not started | - |