Revise debug notes to the literate memoir pattern

[dbosk]

Part of the notes-revision effort (see the tracking issue for the full
per-deck workflow: literate contents.nw conversion, memoir notes,
narrative prose, pedagogical restructuring, \ltnote{} annotations,
LaTeX semantics, LO labels, review).

A draft deck exists on branch debugging-module (last commit 2020-09-28,
pre-modules/ layout: the files sit at debug/slides/ in the repo root;
the merge is clean but the deck must be moved to modules/debug/slides/
afterwards). It covers pdb (multiplier.py) and gdb — and its C++ example
is already literate (multiplier.cpp.nw, woven .tex input into the
deck), so this deck pioneered the approach this whole effort adopts. It
uses the old self-contained Berlin-theme slides template and must be
modernized to the current preamble/contents/notes structure. lecture.md
and issue #237 (research on debugging) are further input material.

Misconceptions input: debugging.tex in vt-prog-misconceptions — documented
misconceptions with critical-aspect analyses and variation patterns to
design activities against (per-deck workflow step 5 in the tracking
issue); matching diagnostic item bank quiz-debugging-{start,end}.json.

Decks

modules/debug/slides

• Literate conversion (contents.nw, chunks replace \inputminted
  line ranges, Makefile + gitignore)
• Memoir notes.tex
• Narrative prose (notes read standalone)
• Pedagogical restructuring (try-first, examples first, variation
  theory)
• \ltnote{} annotations + ltnotes.bib
• LaTeX semantics pass
• Mnemonic LO labels in abstract.tex
• Build + review pass