fix(dashboard): isNew compares timestamps numerically, not by ISO string

ISO strings differing only in millisecond precision or timezone
formatting represent the same instant but failed string equality, so
freshly created documents could miss the "Neu" badge depending on
whatever shape the backend serializer emitted.

Browser specs cannot run in the worktree (birpc WebSocket closure
crash documented in the PR description); the new vitest-browser test
must be verified from a normal checkout.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/lib/shared/dashboard/ReaderRecentDocs.svelte

@@ -12,7 +12,7 @@ interface Props {
 const { documents }: Props = $props();
 
 function isNew(doc: Document): boolean {
-	return doc.createdAt === doc.updatedAt;
+	return new Date(doc.createdAt).getTime() === new Date(doc.updatedAt).getTime();
 }
 </script>