fix(a11y): enhance accessibility for admin user components (#21717)

This commit adds aria-labels to the search inputs, select fields, action buttons, and close buttons on modals across the admin users layout and the site changelog modal for improved screen reader support.

src/lib/components/admin/Users/Groups.svelte

@@ -157,12 +157,14 @@
 				<input
 					class="w-full text-sm py-1 rounded-r-xl outline-hidden bg-transparent"
 					bind:value={query}
+					aria-label={$i18n.t('Search Groups')}
 					placeholder={$i18n.t('Search Groups')}
 				/>
 				{#if query}
 					<div class="self-center pl-1.5 translate-y-[0.5px] rounded-l-xl bg-transparent">
 						<button
 							class="p-0.5 rounded-full hover:bg-gray-100 dark:hover:bg-gray-900 transition"
+							aria-label={$i18n.t('Clear search')}
 							on:click={() => {
 								query = '';
 							}}
@@ -244,6 +246,7 @@
 
 	<button
 		class="flex items-center justify-between rounded-lg w-full transition mt-4"
+		aria-haspopup="dialog"
 		on:click={() => {
 			showDefaultPermissionsModal = true;
 		}}