fix: persist session banner dismissals and add hide-banner setting

- Stop overwriting AI session titles with the "Planning session" fallback
  during cross-tab broadcasts before initialPlan has hydrated on resume.
- Persist SessionNotificationBanner dismissals to localStorage keyed by
  updatedAt so they survive refresh and auto-re-show on the next event.
- Add Settings → Appearance toggle to hide the banner entirely.
- Drop the inner scrollbar on the planning question list; let the outer
  pane handle all scrolling.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/dashboard/src/__tests__/ai-session-store.test.ts

@@ -52,6 +52,8 @@ describe("AiSessionStore", () => {
       projectId,
       createdAt: now,
       updatedAt: now,
+      lockedByTab: null,
+      lockedAt: null,
     };
   }