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/DashboardRecentDocuments.svelte

@@ -5,7 +5,7 @@ import { getLocale } from '$lib/paraglide/runtime.js';
 type Document = {
 	id: string;
 	title: string;
-	documentDate?: string;
+	createdAt?: string;
 	sender?: { id: string; firstName: string; lastName: string };
 };
 
@@ -20,7 +20,7 @@ function formatDate(dateStr: string): string {
 		day: 'numeric',
 		month: 'long',
 		year: 'numeric'
-	}).format(new Date(dateStr + 'T12:00:00'));
+	}).format(new Date(dateStr));
 }
 </script>
 
@@ -37,12 +37,12 @@ function formatDate(dateStr: string): string {
 				>
 					{doc.title}
 				</a>
-				{#if doc.documentDate}
+				{#if doc.createdAt}
 					<span
 						data-testid="doc-date-{doc.id}"
 						class="ml-2 shrink-0 font-sans text-xs text-gray-400"
 					>
-						{formatDate(doc.documentDate)}
+						{formatDate(doc.createdAt)}
 					</span>
 				{/if}
 			</div>