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/chronik/ChronikFuerDichBox.svelte.spec.ts

@@ -40,7 +40,7 @@ describe('ChronikFuerDichBox', () => {
 			onMarkRead: vi.fn(),
 			onMarkAllRead: vi.fn()
 		});
-		const link = document.querySelector('a[href="/chronik?filter=fuer-dich"]');
+		const link = document.querySelector('a[href="/aktivitaeten?filter=fuer-dich"]');
 		expect(link).not.toBeNull();
 	});