docs(19-01): complete WAV tag writer implementation plan

- SUMMARY.md with task commits, deviations, decisions
- STATE.md updated with position, metrics, decisions
- ROADMAP.md updated with phase 19 progress (1/2 plans)
- REQUIREMENTS.md: WAV-01 through WAV-05 marked complete

.planning/ROADMAP.md

@@ -68,7 +68,7 @@
   3. Editing a WAV file's tags does not alter audio playback — the file sounds identical before and after
   4. Existing metadata in the WAV file that wasn't edited (RIFF INFO chunks, bext, cue markers) survives the tag write unchanged
   5. If the app crashes or loses power during a WAV tag write, the original file is intact (not corrupted or truncated)
-**Plans:** 2 plans
+**Plans:** 1/2 plans executed
 
 Plans:
 - [ ] 19-01-PLAN.md — WAV RIFF parser/writer and writeWavTags function
@@ -117,7 +117,7 @@ Plans:
 | 16. Tag Writing & Database Sync | v1.2 | 3/3 | Complete | 2026-03-17 |
 | 17. Single Track Edit | v1.2 | 2/2 | Complete | 2026-03-18 |
 | 18. Batch Edit | v1.2 | 2/2 | Complete | 2026-03-18 |
-| 19. WAV Tag Writer | v1.2.1 | 0/2 | Not started | - |
+| 19. WAV Tag Writer | 1/2 | In Progress|  | - |
 | 20. OGG Vorbis Tag Writer | v1.2.1 | 0/? | Not started | - |
 | 21. Cleanup | v1.2.1 | 0/? | Not started | - |