Dev setup: correct the hook claim, ship an opt-in committed hook

The naming check was documented as an auto-running pre-commit hook,
but .git/hooks is never cloned and no installer existed - a fresh
clone had nothing, and the real enforcement is CI. Say that plainly.
Ship .githooks/pre-commit (LF-pinned) so a dev who wants the local
check can opt in with 'git config core.hooksPath .githooks'; CI stays
the backstop that fails the build on a bad name.

.gitattributes

@@ -3,3 +3,4 @@
 # Shell scripts must stay LF so Git Bash on Windows can run them
 *.sh text eol=lf
 scripts/check-naming-and-style.sh text eol=lf
+.githooks/pre-commit text eol=lf