build: auto-detect latex/dvips and regenerate docs in default make

When latex and dvips are available, the default no-arg "make" now
regenerates the PostScript documentation from its .tex sources into the
build tree; otherwise the pre-built PostScript shipped in the source tree
is used as-is at install time.  Documentation is always available either
way -- installing latex simply refreshes it from source.

configure (scripts/configure.in, regenerated scripts/configure):
* AC_PATH_PROG for latex + dvips; DOCS_TARGET = "docs" only when both are
  found; AC_SUBST(LATEX/DVIPS/DOCS_TARGET).
* Configuration summary prints "LaTeX docs: yes/no".

scripts/defs.mak.in: export LATEX/DVIPS.

Makefile.in:
* all: ... $(DOCS_TARGET) -- pulls in "docs" only when latex was found.
* docs: best-effort -- `make -k` + a warning on failure so a document
  that will not typeset (or a missing texlive package) never fails the
  build; install falls back to the pre-built PostScript for those.

doc/latexfiles/Makefile:
* use ${LATEX}/${DVIPS} from defs.mak.
* the .tex include figures as ../psfigures/*.ps; point the build-tree
  ../psfigures at ${MAGICSRC}/doc/psfigures (no-op in-tree) so latex and
  dvips find them while outputs stay in the build tree.

CI: main.yml and main-aarch64.yml install
texlive-latex-base/-recommended + texlive-fonts-recommended so the Linux
builds exercise doc regeneration (best-effort, never fatal).

README.Tcl: document latex/dvips as an optional prerequisite for docs.

.gitignore: ignore in-tree doc build artifacts (doc/latexfiles/psfiles/,
*.dvi/*.aux/*.log); the pre-built doc/psfiles/ stays tracked.

Verified out-of-tree with TeX Live 2024: configure reports "LaTeX docs:
yes"; `make` regenerates 27/28 documents into the build tree (maint1.tex
has a genuine LaTeX error and falls back), stays exit 0; `make install`
installs the 27 regenerated PostScript from the build tree and maint1
from the source pre-built copy; the source tree is not modified.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

.github/workflows/main-aarch64.yml

@@ -15,7 +15,8 @@ jobs:
       - name: Get Dependencies
         run: |
           sudo apt-get update
-          sudo apt-get install -y tcl-dev tk-dev libcairo-dev
+          sudo apt-get install -y tcl-dev tk-dev libcairo-dev \
+            texlive-latex-base texlive-latex-recommended texlive-fonts-recommended
       - name: Build
         run: |
           ./configure

.github/workflows/main.yml

@@ -13,7 +13,12 @@ jobs:
       - name: Get Dependencies
         run: |
           sudo apt-get update
-          sudo apt-get install -y tcl-dev tk-dev libcairo-dev
+          # tcl/tk + cairo for the build; texlive (latex + dvips) so the default
+          # "make" also regenerates the PostScript documentation.  Docs are
+          # best-effort — a missing texlive package just falls back to the
+          # pre-built PostScript, it does not fail the build.
+          sudo apt-get install -y tcl-dev tk-dev libcairo-dev \
+            texlive-latex-base texlive-latex-recommended texlive-fonts-recommended
       - name: Build
         run: |
           ./configure