feat(chronik-fuer-dich): include annotationId in mention deep-link

Sidebar was constructing /documents/:id?commentId=… without the
annotationId, so clicking a mention there no-op'ed the deep-link
scroll helper. Route the href through buildCommentHref so the
bell and the chronik sidebar produce identical URLs.

Refs #300.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/chronik/ChronikFuerDichBox.svelte.spec.ts

@@ -114,6 +114,25 @@ describe('ChronikFuerDichBox', () => {
 		expect(onMarkRead.mock.calls[0][0]).toEqual(n);
 	});
 
+	it('mention row href includes both commentId and annotationId when annotationId is present', async () => {
+		render(ChronikFuerDichBox, {
+			unread: [
+				notif({
+					id: 'n-link',
+					documentId: 'doc-42',
+					referenceId: 'comment-7',
+					annotationId: 'annot-9'
+				})
+			],
+			onMarkRead: vi.fn(),
+			onMarkAllRead: vi.fn()
+		});
+		const link = document.querySelector(
+			'a[href="/documents/doc-42?commentId=comment-7&annotationId=annot-9"]'
+		);
+		expect(link).not.toBeNull();
+	});
+
 	it('Dismiss button is a sibling of the document link, never nested inside <a>', async () => {
 		render(ChronikFuerDichBox, {
 			unread: [notif({ id: 'x' })],