Fix link-chip keyboard focus and add optional skeleton shimmer toggle

[edehvictor]

Closes #185
Closes #188

Assigned issue tracker references: #182, #184, #185, #188

Changes

• Added an optional disableShimmer UI flag to CreatorSkeleton and CreatorGridSkeleton with a clear static fallback style when enabled.
• Preserved default shimmer behavior when the new flag is off.
• Added keyboard-visible focus styling hook for link-only social action chips via link-action-chip.
• Added high-contrast (orced-colors) focus fallback so keyboard focus remains visible in contrast modes.
• Added tests for shimmer toggle behavior and social chip focus styling hook.

Testing

• Unable to complete Vitest execution in this environment because dependency installation/tooling remained incomplete in the shell (vitest binary unavailable despite repeated install attempts).
• Updated tests are included and ready to run in CI/local dev with a complete pnpm setup.

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