fix(Button,Pagination): activate non-native as-div/span elements on Enter/Space

[sridhar-3009]

Problem

ButtonRoot and PaginationItem render with role="button" and tabindex="0" when used as non-native elements (as="div", as="span"), but have no onKeydown handler. Native <button> activates on Enter/Space automatically; <div role="button"> does not. Keyboard-only users can focus these elements but cannot activate them.

Closes #616.

Solution

Added an onKeydown handler to each component that fires onClick()/select() on Enter or Space. The handler is only wired when as !== 'button' — native buttons keep their default behavior untouched.

function onKeydown (e: KeyboardEvent) {
  if (e.key === 'Enter' || e.key === ' ') {
    e.preventDefault()
    onClick()
  }
}
// in attrs:
'onKeydown': as === 'button' ? undefined : onKeydown,

Note: ToggleRoot already had keyboard handling and was not changed.

[github-actions]

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