hotfix: correct dark theme color for variant selector

[nielslyngsoe]

fix the variant selector so hover uses themes colors (previously it was white in white, so not readable)

[Copilot]

Pull Request Overview

This hotfix updates the variant selector’s hover state to use the correct theme color tokens.

• Replaces --uui-palette-* variables with --uui-color-* tokens for surface and interactive emphasis.
• Ensures hover styling aligns with both light and dark theme designs.

Comments suppressed due to low confidence (1)

src/Umbraco.Web.UI.Client/src/packages/core/workspace/components/workspace-split-view/workspace-split-view-variant-selector.element.ts:598

• Consider adding a matching :focus-visible style alongside :hover to ensure keyboard users receive equivalent visual feedback.

.switch-button:hover {