fix(shared-ui): export calculateFadeOpacity from index

This utility function was used by contacts-web skeletons but wasn't
exported from the main shared-ui package entry point.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/shared-ui/src/index.ts

@@ -35,6 +35,7 @@ export {
 	SkeletonCard,
 	SkeletonGrid,
 	AppLoadingSkeleton,
+	calculateFadeOpacity,
 } from './molecules';
 
 // Feedback

packages/shared-ui/src/molecules/index.ts

@@ -37,6 +37,7 @@ export {
 	SkeletonCard,
 	SkeletonGrid,
 	AppLoadingSkeleton,
+	calculateFadeOpacity,
 } from './loaders';
 
 // Feedback components