fix(notification): prevent iframe navigation — use goto instead of href follow

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

frontend/src/lib/notification/NotificationDropdown.svelte

@@ -1,4 +1,5 @@
 <script lang="ts">
+import { goto } from '$app/navigation';
 import { m } from '$lib/paraglide/messages.js';
 import { relativeTime } from '$lib/shared/utils/time';
 import type { NotificationItem } from '$lib/notification/notifications.svelte';
@@ -129,7 +130,7 @@ let { notifications, onMarkRead, onMarkAllRead, onClose }: Props = $props();
 	<div class="border-t border-line px-4 py-2">
 		<a
 			href="/aktivitaeten"
-			onclick={onClose}
+			onclick={(e) => { e.preventDefault(); onClose(); goto('/aktivitaeten'); }}
 			class="text-xs font-medium text-ink-2 transition-colors hover:text-ink"
 		>
 			{m.chronik_view_all()}