fix(a11y): improve landing preview contrast - #22

Summary

• Improve contrast for the landing-page chat preview's Encrypted label and message timestamp.
• Add explicit light/dark success-ink tokens and preserve the existing accent-muted semantic token.
• Include comparable desktop before/after screenshots for review.

Why

The production landing baseline exposed two contrast failures in the inert visual preview: the success label and the timestamp rendered with opacity over the accent bubble. The new semantic colors calculate to 4.66:1 light / 8.65:1 dark for the success label and 4.74:1 light / 5.03:1 dark for the timestamp.

Lighthouse evidence

Production baseline scores are ordered Performance / Accessibility / Best Practices / SEO:

• /: desktop 94 / 95 / 100 / 100; mobile 90 / 95 / 100 / 100.
• /security/: desktop 100 / 100 / 100 / 100; mobile had one 72 / 100 / 100 / 100 outlier, followed by two 100 / 100 / 100 / 100 runs.
• /app: desktop 100 / 100 / 100 / 58; mobile 94 / 100 / 100 / 58.

On the current local build, the public routes reached Accessibility, Best Practices, and SEO 100 on both viewports. The landing page measured Performance 94 desktop / 79 mobile with CLS 0.132 / 0.094. Performance and CLS did not reach 100; synthetic runs showed substantial variability, so no score was falsified and no UX trade-off was introduced to optimize a nondeterministic result. A font-display hypothesis was tested and removed because it did not improve CLS.

The /app SEO score of 58 is intentional: the authenticated shell is marked noindex/nofollow and must not be indexed as a public page.

Validation

• pnpm lint — passed (127 files)
• pnpm typecheck — passed
• pnpm test — passed (web 138 tests, worker 292 tests)
• pnpm build — passed
• git diff --check — passed
• No database migrations or deployment were performed.

Visual evidence

Before:

After: