Review follow-ups:
- Leonie/UX: 0.55 navy on the sand canvas was ~2.6:1, under the WCAG 1.4.11 3:1
non-text floor for senior readers; 0.7 clears it.
- Sara/QA: add a browser test that actually renders a cross-level link and
asserts the distinct 2 6 dash, and that a non-cross-link parent edge stays
solid — the cadence was previously only validated via the structural
crossLinks array, never where it renders.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>