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 - a fresh clone had nothing and CI is
the real enforcement. Ship .githooks/pre-commit for opt-in local use.

.githooks/pre-commit

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+# Committed pre-commit hook. Activate per clone with:
+#   git config core.hooksPath .githooks
+# Runs the naming/style gate; blocks the commit on failure.
+exec bash "$(git rev-parse --show-toplevel)/scripts/check-naming-and-style.sh"