docs: fix French PDF build with babel-french 4.x (TeX Live 2025)

[grandixximo]

Problem

The package-indep (debian:sid) CI job fails building the French PDF documentation:

Master_Developer.tex:38: The key 'FBsetup/CompactItemize' is unknown
Error: xelatex compilation failed
dh_auto_build: error: cd src && make -j4 docs returned exit code 2

Root cause

babel-french 4.x (TeX Live 2025, now in Debian sid) removed legacy option keys such as CompactItemize, deprecated since babel-french 3.0 (2015). dblatex 0.3.12's dbk_locale.sty still calls \frenchbsetup{CompactItemize=false} from its \babelsetup{fr} hook. The \frenchbsetup macro itself still exists as an alias, so dblatex's \@ifundefined guard passes, but the removed key now raises a fatal l3keys "unknown key" error. This affects any distro shipping TeX Live 2025+; sid is simply the first CI image to carry it.

Fix

In docs/src/emc2.sty (loaded before the hook executes), when the modern \frenchsetup interface is available (babel-french >= 3.0), neutralize the legacy \frenchbsetup macro and apply the documented modern equivalent of CompactItemize=false (StandardItemizeEnv=true, StandardItemLabels=true). Older toolchains keep the previous behavior via the \@ifundefined guard, so bullseye/bookworm/trixie output is unchanged.

Testing

• Reproduced the exact CI failure in a debian:sid container with the pristine style file; the fixed file builds the French test PDF.
• Ran the full CI-equivalent build in debian:sid (debian/configure, apt build-dep --indep-only, debuild --build=all): completes with exit 0, including docs/src/fr/Master_Developer.pdf and the linuxcnc-doc-fr package.