Enable focused tests as repository pre-commit hook

.githooks/pre-commit

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+# Repository pre-commit hook: run only tests selected by staged paths.
+set -euo pipefail
+
+REPO_ROOT="$(git rev-parse --show-toplevel)"
+exec "$REPO_ROOT/scripts/test-changed.sh"