Handle expired session errors gracefully

- Add custom response for 419 (CSRF token expiration) using exception handler.
- Update language files to include localized error messages for expired sessions.

app/application/lang/en/http-statuses.php

@@ -81,4 +81,5 @@ return [
     '598'          => 'Network Read Timeout Error',
     '599'          => 'Network Connect Timeout Error',
     'unknownError' => 'Unknown Error',
+    'csrfError'    => 'It looks like your session has expired. Please try again.',
 ];