fix(#145): deep-link notifications; show createdAt in recent docs

- Notification widget builds full link with ?commentId= and
  &annotationId= params, matching the bell notification behaviour
- Recent docs widget shows createdAt (upload date) instead of
  documentDate (the date on the original document)

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

frontend/src/lib/components/DashboardMentions.svelte

@@ -5,6 +5,8 @@ type NotificationDTO = {
 	id: string;
 	type: 'REPLY' | 'MENTION';
 	documentId?: string;
+	referenceId?: string;
+	annotationId?: string;
 	read: boolean;
 	createdAt: string;
 	actorName?: string;
@@ -26,7 +28,9 @@ let { mentions }: Props = $props();
 			<div class="flex items-center gap-3 border-b border-line py-2 last:border-0">
 				{#if mention.documentId}
 					<a
-						href="/documents/{mention.documentId}"
+						href={mention.annotationId
+							? `/documents/${mention.documentId}?commentId=${mention.referenceId}&annotationId=${mention.annotationId}`
+							: `/documents/${mention.documentId}?commentId=${mention.referenceId}`}
 						class="font-serif text-sm text-ink hover:text-ink-2"
 					>
 						{mention.actorName ?? ''}