Builds on the PR #1957 merge (Zeljko's Vol1 layout), otherwise byte-for-byte his version:
- Remove the end-of-chapter research-questions callouts from all chapters.
- ml_ops correction-cascade figure: keep Zeljko's Model A-D chain TikZ drawing,
and rewrite the caption, alt-text, and lead-in to describe the chain (they
carried a stale 'timeline' description that no longer matched the figure),
plus an operations-impact line.
- Standardize the matplotlib figure font on a bundled TeX Gyre Heros (a free,
redistributable Helvetica-metric clone) registered at runtime in
book/tools/figures/style.py, so figures render with a real bold identically
on macOS, Linux, and CI instead of falling back to DejaVu Sans or an
unreachable macOS .ttc bold face.
Vijay Janapa Reddi