fix(pagination): hide mobile page label from AT tree with aria-hidden

The mobile 'Seite X von Y' span had aria-current='page', which created two
elements announcing the current page on wide screens: the hidden mobile label
and the active desktop button. On sm:+ screens the mobile span is display:none
(removed from AT tree), but on small screens both the span and the desktop
button were redundant.

Replace aria-current with aria-hidden='true' on the mobile label so AT always
relies on the desktop button's aria-current. Updates spec test accordingly and
adds a second assertion in a broader test context (Decision Queue #1).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/Pagination.svelte

@@ -95,9 +95,10 @@ const pageWindow = $derived.by(() => {
 		{/if}
 
 		<!-- Mobile: "Seite X von Y" label (hidden on sm: and above) -->
+		<!-- aria-hidden: desktop numbered buttons carry the aria-current="page" role; this label is redundant on wide screens -->
 		<span
 			data-testid="pagination-page-label"
-			aria-current="page"
+			aria-hidden="true"
 			class="font-sans text-sm text-ink-2 sm:hidden"
 		>
 			{m.pagination_page_of({ page: page + 1, total: totalPages })}