fix: allow REUSE LICENSES/ dir in root-shape allowlist

check-root-shape.sh was rejecting the REUSE-mandated LICENSES/ directory
as root drift because .machine_readable/root-allow.txt never listed it.
Add the canonical entry (matching the already-fixed this-ssg reference).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: hyperpolymath

.machine_readable/root-allow.txt

@@ -22,6 +22,7 @@ MAINTAINERS.adoc           # maintainer roster
 CONTRIBUTING.md            # REQUIRED AT ROOT by scorecard-enforcer/openssf-compliance/quality CI (test -f, no .github fallback). The fuller copy in .github/ is GitHub's auto-discovery convention; dedupe is an owner decision (would need those CI checks updated to accept .github/).
 SECURITY.md                # REQUIRED AT ROOT by scorecard-enforcer CI + the security-policy contractile (test -f SECURITY.md). See CONTRIBUTING.md note re: the .github/ copy.
 LICENSE
+LICENSES/                  # REUSE licence texts (MPL-2.0.txt + CC-BY-SA-4.0.txt) for the dual-licence model (code MPL-2.0 / docs CC-BY-SA-4.0)
 CHANGELOG.md
 
 # ─── Build entry points (must live at root for their tooling) ────────────────