docs: merge adjacent documentation blocks

[Jammy2211]

Summary

• Merges three scanner-confirmed adjacent top-level documentation boundaries across two HowToLens tutorials.
• Preserves every decoded teaching block and its ordering exactly while removing empty notebook-conversion boundaries.
• Contributes to the workspace-wide cleanup tracked by refactor: merge adjacent workspace docstrings autolens_workspace#341.

Scripts Changed

• scripts/chapter_1_introduction/tutorial_3_more_ray_tracing.py — joined two adjacent ray-tracing documentation boundaries.
• scripts/chapter_4_pixelizations/tutorial_5_borders.py — joined the adjacent border/demagnification documentation blocks.

Generated Artifacts

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

Test Plan

• Exact origin/main transform witnesses and Python compilation passed for both scripts.
• Canonical tutorial smoke runner passed 6/6 entries.
• Two generated notebook conversions contain no column-zero marker or triple-quote artifact code cells.
• Workspace-wide Hygiene scan reports zero findings and zero parse errors.

Could not update

• None.

Generated by the PyAutoLabs agent workflow.