relativeTime function
Formats time as a compact relative age from now (e.g. 5m ago,
2h ago, 3d ago). Pure for unit testing — the live caller passes
DateTime.now().
Implementation
String relativeTime(DateTime time, DateTime now) {
final d = now.difference(time);
if (d.isNegative) return 'just now';
if (d.inSeconds < 60) return '${d.inSeconds}s ago';
if (d.inMinutes < 60) return '${d.inMinutes}m ago';
if (d.inHours < 24) return '${d.inHours}h ago';
return '${d.inDays}d ago';
}