feat(app-expo): replay brand splash on logout and route to login

After sign-out or data purge, clear session state reliably, remount the
splash overlay above navigation, and navigate to login instead of tabs so
users no longer briefly land on the chat home screen.

Co-authored-by: Cursor <cursoragent@cursor.com>

app-expo/src/core/providers.tsx

@@ -6,6 +6,7 @@ import { MemoirReadingSettingsProvider } from '@/core/memoir-reading-settings-co
 import { NetworkError } from '@/core/api/types';
 import { tokenManager } from '@/core/auth/token-manager';
 import { config } from '@/core/config';
+import { authKeys } from '@/features/auth/auth-query-keys';
 import { AppQueryProvider, queryClient } from '@/core/query';
 
 /**
@@ -49,8 +50,8 @@ async function refreshTokens(): Promise<boolean> {
  * since the cache flip is the authoritative signal.
  */
 function onAuthFailure() {
-  queryClient.setQueryData(['auth', 'token-check'], false);
-  queryClient.setQueryData(['session'], null);
+  queryClient.setQueryData(authKeys.tokenCheck, false);
+  queryClient.setQueryData(authKeys.session, null);
   tokenManager.clearTokens();
 }