feat(chronik): render commentPreview in ChronikRow; add aria-label for screen readers

Replace the „…" placeholder with {item.commentPreview ?? '„…"'}. Plain-text
binding — no {@html} — as specified in the security note from issue #285.
Adds aria-label to the <a> wrapper for COMMENT_ADDED rows that carry a preview,
giving screen reader users the full context in one announcement.

Generated api.ts updated manually to include commentPreview?:string; will be
regenerated by npm run generate:api once the backend is running.

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

frontend/src/lib/activity/ChronikRow.svelte.spec.ts

@@ -186,6 +186,49 @@ describe('ChronikRow', () => {
 		expect(link).not.toBeNull();
 	});
 
+	// --- commentPreview content ---
+	it('renders commentPreview text when variant is comment and commentPreview is present', async () => {
+		const item: ActivityFeedItemDTO = {
+			...baseItem,
+			kind: 'COMMENT_ADDED',
+			commentPreview: 'Hello family, great letter!'
+		};
+		render(ChronikRow, { item });
+		const preview = document.querySelector('[data-testid="chronik-comment-preview"]');
+		expect(preview).not.toBeNull();
+		expect(preview?.textContent).toContain('Hello family, great letter!');
+	});
+
+	it('renders placeholder ellipsis when variant is comment and commentPreview is null', async () => {
+		const item: ActivityFeedItemDTO = {
+			...baseItem,
+			kind: 'COMMENT_ADDED',
+			commentPreview: undefined
+		};
+		render(ChronikRow, { item });
+		const preview = document.querySelector('[data-testid="chronik-comment-preview"]');
+		expect(preview).not.toBeNull();
+		expect(preview?.textContent?.trim()).toBe('„…"');
+	});
+
+	it('does not render preview paragraph for non-comment variants', async () => {
+		const item: ActivityFeedItemDTO = { ...baseItem, kind: 'TEXT_SAVED' };
+		render(ChronikRow, { item });
+		expect(document.querySelector('[data-testid="chronik-comment-preview"]')).toBeNull();
+	});
+
+	it('link has aria-label containing preview text for comment variant with preview', async () => {
+		const item: ActivityFeedItemDTO = {
+			...baseItem,
+			kind: 'COMMENT_ADDED',
+			commentPreview: 'A wonderful letter from grandma'
+		};
+		render(ChronikRow, { item });
+		const link = document.querySelector('a[aria-label]');
+		expect(link).not.toBeNull();
+		expect(link?.getAttribute('aria-label')).toContain('A wonderful letter from grandma');
+	});
+
 	// --- robustness: title rendering for edge cases ---
 	it('still renders the row link when documentTitle is an empty string', async () => {
 		// Felix: verbText.indexOf(docTitle) returned 0 for empty titles — the span