Restructure NB01: numbered chapters, code gen moved to end with exec

Clean chapter flow:
1. Wie gut ist das Modell? (quiz + failures)
2. Wie bewertet man LLM-Antworten? (5 strategies + live demos)
3. Metriken in der Praxis (F1, composite, tradeoffs)
4. Prompt-Tuning Workshop (interactive text box)
5. Kann das Modell Code schreiben? (generates + executes code)

Removed 'Teil 2' divider, removed orphan cells.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: abossard