Wire future council seats into the plan at M4 and M6

docs/IMPLEMENTATION-PLAN.md

@@ -307,6 +307,12 @@ the reference.
 - Build a bar chart from a dataset in a few clicks; preview live-updates;
   Create → new snippet opens and renders.
 
+**Council** — seat **FT Visual Vocabulary** + **Datawrapper** (chart-choice canon) here:
+this is where Astrolabe stops being a pass-through JSON editor and starts making
+chart-shaped suggestions/defaults, so "_which chart, and why_" becomes a decision the app
+owns — the one thing Carbon's data-viz styling doesn't cover. Seating triggers a one-off
+backfill of the builder's defaults/affordances (see [`/council`](../.claude/skills/council/SKILL.md)).
+
 ---
 
 ## M5 · Settings + Import/Export
@@ -370,6 +376,12 @@ the reference.
 - **A11y:** modal focus trap + return, labelled icon buttons, contrast in both themes (§10).
 - **Offline/installable:** verify the SW + manifest give a working offline + installed app.
 - **About & Privacy** and **Donate** modals.
+- **Council** — seat **web.dev** for the PWA/offline/storage surfaces that 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()`) behind the storage monitor (§02).
+  (The storage-monitor work above is its most concrete consumer; seating triggers a one-off
+  backfill — see [`/council`](../.claude/skills/council/SKILL.md).)
 
 **Manual checks:** keyboard-only run-through; reload restores view from URL;
 offline reload works; install as standalone; reduced-motion honored.