Retroactive-STRIDE audit for Phase 11 (visual-design-responsive-layout-cleanup).
No plan-time threat model existed; register built from implementation files.
All 13 threats closed: 7 mitigated, 6 accepted with documented rationale.
threats_open: 0 — phase 11 security gate passes.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
