feat: add relative time formatter

- Formats DateTime to relative time
- Uses timeago package
- Handles null DateTime

Author: fulleni

lib/shared/utils/date_formatter.dart

@@ -0,0 +1,15 @@
+import 'package:flutter/material.dart';
+import 'package:timeago/timeago.dart' as timeago;
+
+/// Formats the given [dateTime] into a relative time string
+/// (e.g., "5m ago", "Yesterday", "now").
+///
+/// Uses the current locale from [context] to format appropriately.
+/// Returns an empty string if [dateTime] is null.
+String formatRelativeTime(BuildContext context, DateTime? dateTime) {
+  if (dateTime == null) {
+    return '';
+  }
+  final locale = Localizations.localeOf(context).languageCode;
+  return timeago.format(dateTime, locale: locale);
+}