docs(14-01): complete CSS containment & GPU scroll promotion plan

- SUMMARY.md with 2 tasks, 7 files, 3 min duration
- STATE.md updated with plan position, metrics, decisions
- ROADMAP.md updated with plan progress (2/4)

.planning/ROADMAP.md

@@ -120,7 +120,7 @@ Plans:
   3. Render hot paths (renderTrackRow, renderTrackItem) create zero new closures per frame — all event handling uses delegation
   4. Store notifications are batched (queueMicrotask) and components only re-render when their relevant data changes
   5. A profiling guide documents how to diagnose performance issues using pprof (backend) and DevTools (frontend)
-**Plans:** 1/4 plans executed
+**Plans:** 2/4 plans executed
 Plans:
 - [ ] 14-01-PLAN.md — CSS containment + GPU layer promotion on all scroll containers
 - [ ] 14-02-PLAN.md — View caching navigation system (replace innerHTML destruction)
@@ -144,7 +144,7 @@ Plans:
 | 11. Per-Library Scan Pipeline | 3/3 | Complete    | 2026-03-09 | - |
 | 12. Library CRUD & Data Integrity | v1.1 | 1/2 | In Progress | - |
 | 13. Library Views & Phantom Tracks | v1.1 | 0/? | Not started | - |
-| 14. Performance Optimization | 1/4 | In Progress|  | - |
+| 14. Performance Optimization | 2/4 | In Progress|  | - |
 
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 *Roadmap created: 2026-02-27*