fix(review): address review blockers from PR #475

- CommentData.java: add @Nullable on annotationId to match codebase convention
- DashboardService: isEmpty() → isBlank() for commentPreview null-guard
- ChronikRow.svelte: always set aria-label on comment rows (not only when preview present)
- ChronikRow.svelte.spec.ts: add test for aria-label on comment row without preview

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

frontend/src/lib/activity/ChronikRow.svelte

@@ -108,8 +108,10 @@ const rowHref: string = $derived(
 <a
 	href={rowHref}
 	data-variant={variant}
-	aria-label={variant === 'comment' && item.commentPreview
-		? `${m.chronik_comment_added({ actor: actorName, doc: docTitle })} — ${item.commentPreview}`
+	aria-label={variant === 'comment'
+		? item.commentPreview
+			? `${m.chronik_comment_added({ actor: actorName, doc: docTitle })} — ${item.commentPreview}`
+			: m.chronik_comment_added({ actor: actorName, doc: docTitle })
 		: undefined}
 	class="group flex items-start gap-3 p-3 transition-colors hover:bg-muted/50 focus-visible:ring-2 focus-visible:ring-focus-ring focus-visible:outline-none
 		{variant === 'for-you' ? 'border-l-[3px] border-accent bg-accent-bg/10' : ''}"