feat(layout): mount ConfirmDialog in root layout and provide confirm service

provideConfirmService() sets up context for the entire component tree.
ConfirmDialog is mounted once at the bottom of the layout shell.

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

frontend/src/routes/+layout.svelte

@@ -7,9 +7,15 @@ import ThemeToggle from '$lib/components/ThemeToggle.svelte';
 import NotificationBell from '$lib/components/NotificationBell.svelte';
 import AppNav from './AppNav.svelte';
 import UserMenu from './UserMenu.svelte';
+import ConfirmDialog from '$lib/components/ConfirmDialog.svelte';
+import { provideConfirmService } from '$lib/services/confirm.svelte.js';
 
 let { children, data } = $props();
 
+// Provide the confirmation service to the entire component tree.
+// ConfirmDialog below reads it via getConfirmService() and renders the <dialog>.
+provideConfirmService();
+
 const isAdmin = $derived(
 	data?.user?.groups?.some((g: { permissions: string[] }) => g.permissions.includes('ADMIN'))
 );
@@ -70,4 +76,7 @@ const userInitials = $derived.by(() => {
 	<main class={isAuthPage ? '' : 'py-6'}>
 		{@render children()}
 	</main>
+
+	<!-- Shared confirmation dialog — used by getConfirmService() throughout the app -->
+	<ConfirmDialog />
 </div>