chore(gitflow): regenerate installed pre-commit hook to include job7 gitleaks backstop

Root cause: job7/17bdd08 added the gitleaks scan to the hook GENERATOR
(_gitflow_emit_pre_commit) but the installed .githooks/pre-commit is only
(re)written by 'gitflow init'/'install-hook' — never invoked on this repo after
job7. No mechanism propagates a generator change to already-installed hooks, and
T10 diffs only the allow/block verdict (not content), so the drift was silent.
The installed hook (620071b, 2026-06-29) predated the gitleaks addition by 8 days.

Regenerated via 'gitflow.sh install-hook'; installed hook now == fresh emit.
Gates: grep -c gitleaks=7; negative test (staged AKIA... on a working branch)
BLOCKED with exit 1; make test GREEN. Review finding A2 (P0). A content-drift
assertion is added to make test in the fil-rouge commit.

.githooks/pre-commit

@@ -7,6 +7,19 @@ br=$(git symbolic-ref --short -q HEAD 2>/dev/null)
 git rev-parse --verify -q HEAD >/dev/null 2>&1 || exit 0   # root commit — allow
 [ -f "$gd/MERGE_HEAD" ] && exit 0                          # merge in progress — allow
 
+# Secret backstop (job7) — any branch, not just protected ones. Non-blocking
+# if gitleaks isn't installed; auto-discovers ./.gitleaks.toml (repo root).
+if command -v gitleaks >/dev/null 2>&1; then
+  if ! gitleaks git --staged --no-banner >/dev/null 2>&1; then
+    echo "gitflow pre-commit: BLOCKED — gitleaks found a secret in staged changes." >&2
+    echo "  Details: gitleaks git --staged --no-banner" >&2
+    echo "  Genuine false-positive? add an allowlist rule to .gitleaks.toml — never bypass with --no-verify." >&2
+    exit 1
+  fi
+else
+  echo "gitflow pre-commit: gitleaks not installed — secret scan skipped (https://github.com/gitleaks/gitleaks)." >&2
+fi
+
 case "$br" in
   main|develop) ;;                        # protected — keep checking
   *) exit 0 ;;                                              # working branch — allow