survive session-bundle rebuild in chat, feeds, prefs, and age assurance

Review fixes (PR #11182 round 2). Client identity is no longer stable
across token refresh - on web, a cross-tab sync rebuilds the bundle and
disposes the old clients (whose fetch now throws) - so anything that
captured a client at construction time must re-point at the live one:

- MessagesEventBus and Convo get updateClient(); providers sync it via
  effect. No remount, so poll cursors and optimistic pendingMessages
  survive.
- FeedAPI implementations get setClient(); the post-feed queryFn and
  pollLatest re-point page-held apis before fetching (Merge/Home apis
  are stateful across pages, so they cannot be rebuilt per fetch).
- usePreferencesQuery applies fetched labeler dids to the live appview
  client (applyLabelersToClient, factored from session/moderation),
  restoring the old BskyAgent.getPreferences header side effect.
- ageAssurance redirect overlay/dialog polling is mount-only with
  render-synced refs; a client swap mid-poll no longer latches the
  unmounted flag and strands the overlay.
- Convo message-failure classification defers to lex's shouldRetry()
  instead of treating all status-less errors as recoverable.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/lib/api/feed/list.ts

@@ -18,6 +18,10 @@ export class ListFeedAPI implements FeedAPI {
     this.params = feedParams
   }
 
+  setClient(client: Client) {
+    this.client = client
+  }
+
   async peekLatest(): Promise<app.bsky.feed.defs.FeedViewPost> {
     const res = await this.client.call(app.bsky.feed.getListFeed, {
       ...this.params,