Seat web.dev on the design council; record PWA backfill

docs/IMPLEMENTATION-PLAN.md

@@ -437,11 +437,13 @@ entries).
   `DONATE_URL` pending the real link).
 - **Offline/installable:** verify the SW + manifest give a working offline + installed app.
   **⏳ Remaining** — needs manual verification in a running/installed app.
-- **Council** — seat **web.dev** for the PWA/offline/storage surfaces none of the seated
+- **Council** — ~~seat **web.dev** for the PWA/offline/storage surfaces none of the seated
   members cover: the service-worker **update-available** prompt (`registerType: 'prompt'`),
   storage **persistence** (`navigator.storage.persist()`), and the quota **estimate**
-  (`StorageManager.estimate()`). **⏳ Remaining** (storage monitor is its consumer; seating
-  triggers a one-off backfill — see [`/council`](../.claude/skills/council/SKILL.md)).
+  (`StorageManager.estimate()`)~~ ✅ seated + backfilled (update-prompt toast + `persist()`
+  request; estimate already wired). **⏳ Remaining gap:** manifest ships no icons → not yet
+  installable (design-asset task). See [`/council`](../.claude/skills/council/SKILL.md) and
+  [arch 10](architecture/10-interaction-and-feedback.md).
 
 **Manual checks:** keyboard-only run-through; reload restores view from URL;
 offline reload works; install as standalone; reduced-motion honored. **⏳ Still owed**