Sortable header cells: localizable sort labels and Space activation

Version: mantine-datatable 9.2.2

Two small accessibility gaps in the sortable header cell (DataTableHeaderCell):

1. The sort state is announced in English only. The icon wrapper carries aria-label="Not sorted" / "Sorted ascending" / "Sorted descending". There is no prop to change these strings, unlike noRecordsText, loadingText or recordsPerPageLabel. sortIcons replaces the icon but keeps the English label around it. For a non-English UI, screen reader users hear a mix of languages.

2. Space does not activate the header. The cell is rendered with role="button" and tabIndex={0}, but onKeyDown only handles Enter. Space is the other standard activation key for buttons; pressing it does nothing and scrolls the page.

Suggested API

• A sortLabels prop (or similar) with { unsorted, ascending, descending } strings, defaulting to the current English ones.
• Handle ' ' alongside 'Enter' in the header cell's onKeyDown, with preventDefault() so the page does not scroll.
• Optionally, aria-sort on the <th>; note that with role="button" on the cell the columnheader role is overridden, so this may need the button role moved to an inner element.

Happy to open a PR if the shape is acceptable.

Start at the DataTableHeaderCell implementation and trace how its sortable icon labels and onKeyDown handler are wired. Add configurable unsorted, ascending, and descending labels while preserving the current defaults, and make Space activate sorting without scrolling. Done means localized labels are exposed through the component API and both Enter and Space behave as standard activation keys.