Adds structure for the three Hueber Deutsch üben books (Wortschatz &
Grammatik, Hören & Sprechen, Lesen & Schreiben A1), kept separate from
the Menschen A1.1 lesson files since they're organized by topic/unit
rather than a shared lesson curriculum.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
