Add validation coverage for pure-black theme and provider flow

[georgewrmarshall]

Description

Add automated and manual verification coverage across tokens, providers, components, and Storybook proofs.

Acceptance Criteria

• Tests cover theme/provider branching where practical
• Storybook/manual verification exists for web and RN
• Affected package build, test, and lint checks pass

Constraint

• isPureBlack=false uses the existing grey dark theme
• isPureBlack=true uses pureBlackDarkTheme

References

• Jira epic: TMCU-622