chore: complete pyprojroot boilerplate removal in tutorial_1_models

Follow-up to the April 13 pyprojroot cleanup which removed the boilerplate
from most workspace scripts but missed
scripts/chapter_1_introduction/tutorial_1_models.py.

Removes the standard pyprojroot magic-cell stub plus the matching
"PyProjRoot" docstring section that introduced it.

Notebook regenerated to match.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 2 people