Controles bilingües / bilingual quizzes

Canonical bank (packaged for Colab/PyPI):
  src/didactichem/data/controles/es
  src/didactichem/data/controles/en

Repo mirror (optional on Drive):
  notebooks/controles/es
  notebooks/controles/en

Regenerate BOTH languages:
  python scripts/generar_controles.py

Student notebooks use didactichem.controles_dir() (package data first).
