Makefile slides target broken after slides.tex → slides-intro.tex rename

[dbosk]

Context

While updating CLAUDE.md to reflect the current repo state, I noticed the
slides.pdf build target no longer matches the source file on disk.

Observation

In commit 06f9ea8 ("Adds Java tutorial", 2025-11-07), src/slides.tex was
renamed to src/slides-intro.tex (a R100 identity rename). The Makefiles
were not updated to match:

• src/Makefile:2 — all: lpbook.pdf lpbook-teachers.pdf slides.pdf
• src/Makefile:47-48 — slides.pdf: slides.tex didactic.sty
• src/Makefile:69 — ${RM} lpbook.pdf lpbook-teachers.pdf slides.pdf
• Makefile:6 (top-level) — release_files=src/lpbook.pdf src/lpbook-teachers.pdf src/slides.pdf

Running make -C src slides.pdf from a clean checkout would fail because
slides.tex no longer exists.

Why it matters

• make (the default target) and make publish both depend on slides.pdf,
  so the entire release path is currently broken.
• An untracked src/slides-tutorial-java.pdf suggests there may eventually
  be a second slide deck (slides-tutorial-java.tex?), in which case the
  rename of slides.pdf → slides-intro.pdf is the right direction.

Evidence

$ git log --all --follow --name-status -- src/slides-intro.tex | head -3
06f9ea8 Adds Java tutorial
R100  src/slides.tex  src/slides-intro.tex

$ ls src/slides*.tex
src/slides-intro.tex

Suggested follow-up

1. Rename build targets in src/Makefile and the top-level Makefile:
   • slides.pdf → slides-intro.pdf
   • slides.tex → slides-intro.tex
2. If slides-tutorial-java.tex is intended to exist, add it as a sibling
   target in the same commit.
3. Update the matching clean rule and the release_files list.