fix(client): preserve prefs on logout; recover from initial-sync failure (N98/N99)

- N98: logoutClient and handleLogout now call removeFallbackSession() (removes
  only the 4 session credential keys) instead of window.localStorage.clear(),
  so settings, unsent drafts, PiP position, and status are preserved across a
  normal logout. localStorage.clear() stays reserved for clearLoginData() (the
  explicit factory-reset path).
- N99: the useSyncState callback now handles ERROR/STOPPED. A sync failure
  before the first PREPARED (offline at startup, homeserver unreachable) shows
  a dedicated error splash with a Retry button (startMatrix) instead of an
  endless "Heating up" spinner alongside a contradictory "Connection Lost!"
  banner. Guarded by a hasPreparedRef so post-PREPARED transient errors still
  go through <SyncStatus>; PREPARED self-heals the splash on recovery, and the
  redundant banner is suppressed while the splash is shown.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/client/initMatrix.ts

@@ -2,6 +2,7 @@ import { createClient, MatrixClient, IndexedDBStore, IndexedDBCryptoStore } from
 
 import { cryptoCallbacks } from './secretStorageKeys';
 import { clearNavToActivePathStore } from '../app/state/navToActivePath';
+import { removeFallbackSession } from '../app/state/sessions';
 import { pushSessionToSW } from '../sw-session';
 
 type Session = {
@@ -75,7 +76,9 @@ export const logoutClient = async (mx: MatrixClient) => {
     // ignore if failed to logout
   }
   await mx.clearStores();
-  window.localStorage.clear();
+  // Remove only the session credential keys, preserving user preferences and
+  // unsent drafts (N98). The factory-reset path is clearLoginData() below.
+  removeFallbackSession();
   window.location.reload();
 };