docs(16-02): complete FLAC tag writer plan

- Create 16-02-SUMMARY.md with execution results
- Update STATE.md with Phase 16 progress and decisions
- Update ROADMAP.md plan progress
- Mark WRITE-02 and WRITE-04 requirements complete

.planning/ROADMAP.md

@@ -72,7 +72,7 @@ Plans:
   3. Cover art images (JPEG/PNG) can be embedded in both MP3 and FLAC files — the embedded image is readable back and the existing cover art pipeline (extraction, thumbnails) works with the newly embedded art
   4. After a tag write, the database reflects the new metadata within the same operation: artist/album/genre entities are created or relinked (never mutated in-place), orphaned entities with zero remaining references are cleaned up, and the FTS5 index is updated — no library rescan needed
   5. If the currently-playing track is being edited, playback is stopped before the file write begins — the user does not experience a crash or corrupted audio stream
-**Plans:** 3 plans
+**Plans:** 1/3 plans executed
 Plans:
 - [ ] 16-01-PLAN.md — Tagwriter foundation + sqlc queries + MP3 writer (Wave 1)
 - [ ] 16-02-PLAN.md — FLAC writer with go-flac ecosystem (Wave 1)
@@ -129,7 +129,7 @@ Plans:
 | 13. Library Views & Phantom Tracks | v1.1 | 2/2 | Complete | 2026-03-16 |
 | 14. Performance Optimization | v1.1 | 4/4 | Complete | 2026-03-15 |
 | 15. Schema Migration & Write Safety | 2/2 | Complete    | 2026-03-16 | - |
-| 16. Tag Writing & Database Sync | v1.2 | 0/3 | Not started | - |
+| 16. Tag Writing & Database Sync | 1/3 | In Progress|  | - |
 | 17. Single Track Edit | v1.2 | 0/? | Not started | - |
 | 18. Batch Edit | v1.2 | 0/? | Not started | - |
 | 19. OGG Vorbis Tag Writing | v1.2 | 0/? | Not started | - |