fix(auth): resolve race condition causing files not to load on initial visit

The cached-user-data path in checkAuthentication() fired resolveHomeFolder()
and loadFiles() concurrently with refreshUserData() using non-blocking .then()
chains. When the session cookie was expired, the folder/file API calls received
401 errors before the session could be refreshed. Now awaits session validation
before loading files.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/interfaces/api/handlers/auth_handler.rs

@@ -674,4 +674,4 @@ async fn oidc_exchange(
     );
     cookie_auth::append_csrf_cookie(response.headers_mut(), auth_response.expires_in);
     Ok(response)
-}
+}