refactor(comment): remove dead findAnnotationIdsByIds; fix aria-label i18n; rename misleading test

- Remove `findAnnotationIdsByIds` from CommentService — no production caller exists now
  that DashboardService uses `findDataByIds` directly; along with its test coverage
- Fix aria-label construction in ChronikRow: pass actorName to i18n message function
  instead of manually prepending the actor, so all locales render correctly
- Rename `findDataByIds_does_not_truncate_at_exactly_120_chars` →
  `findDataByIds_preserves_content_at_exactly_120_chars` for accurate description

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

frontend/src/lib/activity/ChronikRow.svelte

@@ -109,7 +109,7 @@ const rowHref: string = $derived(
 	href={rowHref}
 	data-variant={variant}
 	aria-label={variant === 'comment' && item.commentPreview
-		? `${actorName} ${m.chronik_comment_added({ actor: '', doc: docTitle }).trim()} — ${item.commentPreview}`
+		? `${m.chronik_comment_added({ actor: actorName, doc: docTitle })} — ${item.commentPreview}`
 		: 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' : ''}"