feat: support scheme outline colors

[e-simpson]

Summary

This PR extends the semantic scheme: modifier to outline colors while preserving #14's integer and arbitrary opacity handling.

Dependency / merge order

Please merge #14 first, then #15.

This draft branch is now intentionally stacked on #14 so the combined implementation and conflict resolution are already tested. Until #14 lands, GitHub shows both commits in this PR. After #14 is merged into main, the base diff reduces to the outline-specific change.

Changes

• Recognizes outline-* color utilities in scheme expansion.
• Excludes outline widths, offsets, styles, outline-hidden, and non-color arbitrary values.
• Preserves integer and arbitrary opacity suffixes:

<View className="scheme:outline-brand/25" />
<View className="scheme:outline-brand/[.37]" />

• Keeps configurable dark/light suffixes and both-variant validation.
• Documents outline scheme support.

Validation

• bun run spec -- src/parser/modifiers.test.ts src/parser/colors.test.ts — 167 passed
• bun run check
• bun run lint
• bun run format:check