feat(linter): add opt-in color-blind contrast lint rule

[mvanhorn]

Summary

design.md lint checks component backgroundColor/textColor pairs against WCAG AA as perceived by full-color vision. This adds an opt-in color-blind-contrast rule, enabled with a new --cvd flag, that re-runs the contrast check under simulated protanopia, deuteranopia, and tritanopia and warns when a simulated pair drops below 3:1. It is off by default, so existing lint output is unchanged.

Why this matters

A pair that clears AA for full-color vision can still collapse for the roughly 5-10% of users with congenital color-vision deficiency, because the only cue is a hue shift those users do not see. The worked example from #48: brand orange #E44001 on white is 4.17:1, an AA near-miss the baseline rule already reports, but 2.92:1 under protanopia and 2.31:1 under deuteranopia. The opt-in rule surfaces exactly those two failures the default check never sees.

Demo

Simulated Demo (HyperFrames):

Changes

• The color-blind-contrast rule mirrors the existing contrast-ratio rule and reuses parseColor/contrastRatio for the simulated colors, so there is no duplicated color math. Simulation applies the Brettel-Vienot-Mollon matrices to each ResolvedColor, then re-parses the result to recover WCAG luminance.
• The opt-in lives entirely in the CLI: --cvd composes the rule onto DEFAULT_RULE_DESCRIPTORS for that run. The rule is exported for selective composition but deliberately kept out of the default set, so default lint output is byte-identical.

Testing

• bun test: 285 pass, 1 skip, 0 fail. New tests cover the Feature: color-blind contrast lint rule (opt-in, Brettel-Viénot-Mollon simulation) #48 worked example, a CVD-safe pair, and the rule's absence from the default rule set.
• bun run lint and bun run build pass clean.
• Dogfooded: design.md lint --cvd on a #E44001-on-white button reproduces the issue's exact figures (protanopia 2.92:1 on #9d9c10, deuteranopia 2.31:1 on #a7b314); without --cvd the output is unchanged.

Fixes #48

[rajpratham1]

This is a thoughtful accessibility enhancement that introduces an opt-in color-blind contrast lint rule without changing the default linting behavior. The implementation is modular, integrates cleanly with the existing rule system, exposes the feature through a CLI flag, and includes good test coverage to verify both the rule itself and that it remains disabled by default.