fix(app): raise muted ink tokens to WCAG AA in both colour schemes

[jdjioe5-cpu]

What and why

Closes #38.
Audited and repaired landing-page step labels, footer disclaimer, and \LagNotice\ text contrast to strictly comply with WCAG AA body copy contrast requirements ($\ge 4.5:1$) in both light and dark colour schemes, replacing fragile and failing raw ink opacities (\ ext-ink/50\ and \ ext-ink/60) with semantic tokens.

Changes

• \�pp/globals.css:
  • Defined --muted: #525a56;\ in light mode (relative luminance 0.0992, contrast ratio 6.54:1 against --paper: #f6f7f5).
  • Defined --muted: #949f99;\ in dark mode (relative luminance 0.3380, contrast ratio 6.74:1 against --paper: #0f1512).
  • Registered --color-muted: var(--muted);\ under Tailwind v4 @theme\ so \ ext-muted\ is universally available.
  • Added documentation comments in \globals.css\ detailing palette rules and WCAG constraints to prevent regressions.
• \�pp/(marketing)/page.tsx:
  • Replaced \ ext-ink/50\ in step numbers with \ ext-muted.
  • Replaced \ ext-ink/60\ in footer disclaimer with \ ext-muted.
• \components/indexer/LagNotice.tsx:
  • Replaced \ ext-ink/60\ with \ ext-muted.
• \lib/contrast.test.ts:
  • Added 49 unit tests implementing exact WCAG 2.1 relative luminance and contrast ratio formulas.
  • Verified --muted\ achieves $\ge 4.5:1$ in both light and dark modes.
  • Proved that previous raw opacities failed or skirted the threshold on light paper: \ ext-ink/50\ composited is 3.30:1 (fails AA), and \ ext-ink/60\ is 4.54:1 (dangerously fragile).
  • Added an automated codebase scan guarding \�pp/\ and \components/\ against any reintroduction of \ ext-ink/50\ or \ ext-ink/60.
• \ROADMAP.md:
  • Added Changelog entry; \M3-17\ remains \IN PROGRESS\ pending remaining keyboard navigation and focus enhancements.

Hard rules / invariants touched

• AGENTS.md §8.3 (Accessibility as required; contrast ratio $\ge 4.5:1$ for body copy).
• Invariant numbers: none (no contract, auth, or claim-link-fragment logic touched).

Measured Contrast Ratios

• Light mode (--paper: #f6f7f5):
  • --ink: #141a17: 16.42:1 (WCAG AA pass)
  • --muted: #525a56: 6.54:1 (WCAG AA pass $\ge 4.5:1$)
  • (Previous \ ext-ink/50\ equivalent: 3.30:1 — failed)
  • (Previous \ ext-ink/60\ equivalent: 4.54:1 — fragile)
• Dark mode (--paper: #0f1512):
  • --ink: #e8ede9: 15.60:1 (WCAG AA pass)
  • --muted: #949f99: 6.74:1 (WCAG AA pass $\ge 4.5:1$)

Tests

All verification commands executed locally and passed with zero errors or warnings:

\
$ pnpm lint

biome check .
Checked 84 files in 21ms. No fixes applied.

$ pnpm typecheck

tsc --noEmit

$ pnpm test

vitest run
Test Files 16 passed (16)
Tests 215 passed (215)
Duration 820ms

$ pnpm build

next build
▲ Next.js 16.3.8 (Turbopack)
✓ Compiled successfully in 478ms
✓ Generating static pages using 14 workers (6/6) in 448ms
Finalizing page optimization ...
\\

Docs / ADR

• Updated \�pp/globals.css\ with design palette and WCAG documentation.
• Updated \ROADMAP.md.

Roadmap

• \M3-17\ (status unchanged, \IN PROGRESS).
• Changelog entry added: yes.

Assumptions and open questions

None. Diff strictly respects project structure boundaries and introduces zero new dependencies.