nx_uiq_contrast_gate.nx

nx_uiq_contrast_gate.nx -- KAT gate for the computed WCAG contrast auditor. Proves (before any page is judged): the WCAG math matches the W3C reference (21.00 / 4.54), the CSS color parser handles rgb()/hex, the audit is NON-VACUOUS (catches a real #999-on-#fff = 2.85:1 fail), and it does NOT false-positive on a page with no color tokens. Deterministic sovereign gate (nx_cc->nxasm). license_tier: ORIGINAL expect_exit: 0