refactor(admin): replace window.confirm with ConfirmService in admin group delete

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

frontend/src/routes/admin/groups/[id]/+page.svelte

@@ -2,12 +2,24 @@
 import { enhance } from '$app/forms';
 import { beforeNavigate, goto } from '$app/navigation';
 import { m } from '$lib/paraglide/messages.js';
+import { getConfirmService } from '$lib/services/confirm.svelte.js';
 
 let { data, form } = $props();
 
+const { confirm } = getConfirmService();
+
 let isDirty = $state(false);
 let showUnsavedWarning = $state(false);
 let discardTarget: string | null = $state(null);
+let deleteFormEl = $state<HTMLFormElement | null>(null);
+
+async function handleDelete() {
+	const confirmed = await confirm({
+		title: m.admin_group_delete_confirm(),
+		destructive: true
+	});
+	if (confirmed) deleteFormEl!.requestSubmit();
+}
 
 beforeNavigate(({ cancel, to }) => {
 	if (isDirty) {
@@ -59,18 +71,10 @@ const ADMIN_PERMISSIONS = $derived([
 		<h2 class="flex-1 font-sans text-sm font-bold text-ink">
 			{m.admin_group_edit_heading({ name: data.group.name })}
 		</h2>
-		<form
-			method="POST"
-			action="?/delete"
-			use:enhance={({ cancel }) => {
-				if (!confirm(m.admin_group_delete_confirm())) cancel();
-				return async ({ update }) => {
-					await update();
-				};
-			}}
-		>
+		<form bind:this={deleteFormEl} method="POST" action="?/delete" use:enhance>
 			<button
-				type="submit"
+				type="button"
+				onclick={handleDelete}
 				class="rounded-sm border border-red-200 bg-red-50 px-3 py-1.5 font-sans text-xs font-bold tracking-widest text-red-700 uppercase transition-colors hover:bg-red-100 dark:border-red-800 dark:bg-red-950/40 dark:text-red-400 dark:hover:bg-red-950/60"
 			>
 				{m.btn_delete()}