fix(data-table): sync pinned column hover transition

[IzumiSy]

Motivation

Pinned DataTable body cells use their own opaque background so horizontally scrolled content does not bleed through sticky columns. Their hover and selected colors were updated at the cell level with group-hover, while the rest of the row relied on the row-level transition-colors style.

That mismatch made pinned columns snap to the hover color slightly earlier than scrollable columns, which was noticeable in the DataTable lab and made the row feel visually inconsistent.

This behavior belongs to the in-flight pinned-column work and is already covered by that unreleased feature's existing changeset.

Design Decision

Chosen approach

Add transition-colors to pinned body cells so their background color animates with the same timing as the rest of the row.

Alternatives considered

Changing the row hover implementation would have touched all table cells. This fix stays local to the sticky-cell path, which is the only place the timing diverged.

Summary

• add transition-colors to pinned DataTable body cells
• keep the existing sticky background and hover color logic intact
• rely on the existing unreleased pinned-column changeset instead of adding a new one