feat(chronik): rename route and heading to Aktivitäten

/chronik → /aktivitaeten; heading updated in all three locales.
Component folder (lib/components/chronik/) stays unchanged — internal
implementation detail, not user-facing.

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

frontend/src/lib/components/NotificationDropdown.svelte

@@ -128,7 +128,7 @@ let { notifications, onMarkRead, onMarkAllRead, onClose }: Props = $props();
 
 	<div class="border-t border-line px-4 py-2">
 		<a
-			href="/chronik"
+			href="/aktivitaeten"
 			onclick={onClose}
 			class="text-xs font-medium text-ink-2 transition-colors hover:text-ink"
 		>