Add runtime color utilities and contrast validation

[Jason Morse (JasonVMo)]

Summary

• add the opt-in @fluentui-react-native/design/color-lib runtime entry point for literal color parsing, sRGB/OKLCH conversion, alpha compositing, WCAG contrast ratios, and default or Bebop Warm hover/pressed generation
• preserve authored interaction values and return structured diagnostics when native or dynamic React Native colors cannot be resolved in JavaScript
• export WCAG policy, semantic pairings, structured audits, and result filters from the existing test-only @fluentui-react-native/design/testing entry point
• keep pinned default and Bebop Warm conformance fixtures internal to package tests, with existing upstream contrast failures recorded explicitly
• keep the production design root free of color-lib; measure only the runtime subpath and omit testing-only validation from bundle-size scenarios

Design alignment

The algorithms and conformance data were verified with the jasonmo_microsoft EMU identity against x3-design/fluent-design@d334acf5cbad813f2b7cd554da942b09a7ff8f10. Separate 118-value fixtures cover the default and Bebop Warm base themes across light/dark hover and pressed states.

Validation

• design package format, lint, build, and Jest suites
• root TypeScript build and no-cache Lage test suite
• full Lage lint and Markdown link checks
• repository structural, publishing, and changeset checks
• macOS and Windows Metro bundle measurements for production scenarios

Fixes #4268
Fixes #4262

[github-actions]

Bundle size report

Tree-shaken production Metro bundles. Component costs are relative to their platform shell; shell costs are absolute.

Platform	Scenario	Baseline cost	Current cost	Cost delta	Change	Gzip delta	Module delta
macos	shell	801.3 KiB	801.3 KiB	0.0 KiB	0.00%	0.0 KiB	+0
macos	components-button	50.1 KiB	50.2 KiB	+0.1 KiB	+0.26%	+0.0 KiB	+2
macos	components-catalog	267.3 KiB	273.3 KiB	+6.0 KiB	+2.24%	+2.1 KiB	+9
macos	design-theme-state	33.3 KiB	33.4 KiB	+0.1 KiB	+0.40%	+0.1 KiB	+2
macos	design-color-lib	New	7.1 KiB	New	New	New	New
macos	design-theme-state-legacy-source	35.3 KiB	35.5 KiB	+0.1 KiB	+0.38%	+0.0 KiB	+2
macos	design-legacy-theme-from-flex	100.2 KiB	100.4 KiB	+0.1 KiB	+0.13%	+0.1 KiB	+2
windows	shell	810.2 KiB	810.2 KiB	0.0 KiB	0.00%	0.0 KiB	+0
windows	components-button	50.0 KiB	50.1 KiB	+0.1 KiB	+0.26%	+0.0 KiB	+2
windows	components-catalog	267.0 KiB	273.0 KiB	+6.0 KiB	+2.24%	+2.1 KiB	+9
windows	design-theme-state	33.2 KiB	33.3 KiB	+0.1 KiB	+0.41%	+0.1 KiB	+2
windows	design-color-lib	New	7.1 KiB	New	New	New	New
windows	design-theme-state-legacy-source	35.3 KiB	35.4 KiB	+0.1 KiB	+0.38%	+0.0 KiB	+2
windows	design-legacy-theme-from-flex	100.0 KiB	100.1 KiB	+0.1 KiB	+0.13%	+0.1 KiB	+2

The job is advisory: size changes are reported but do not fail the pull request. Bundle or analysis errors still fail.

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