docs: merge adjacent documentation blocks

[Jammy2211]

Summary

• Merges the scanner-confirmed adjacent top-level documentation boundary in the practical modeling tutorial.
• Preserves the decoded teaching prose and section ordering exactly while removing the empty notebook-conversion boundary.
• Contributes to the workspace-wide cleanup tracked by refactor: merge adjacent workspace docstrings autolens_workspace#341.

Scripts Changed

• scripts/chapter_2_modeling/tutorial_2_practicalities.py — joined the adjacent practicalities documentation sections.

Generated Artifacts

• Regenerated notebooks and the tutorial navigator catalogue from the updated script.

Test Plan

• Exact origin/main transform witness and Python compilation passed.
• Canonical tutorial smoke runner passed 4/4 entries.
• Generated notebook contains no column-zero marker or triple-quote artifact code cell.
• Workspace-wide Hygiene scan reports zero findings and zero parse errors.

Could not update

• None.

Generated by the PyAutoLabs agent workflow.