Add friends leaderboard, reverse button in add page

lib/services/data_service/data_service_core.dart

@@ -108,6 +108,10 @@ class DataService extends ChangeNotifier {
   bool get isHomepageLoading => _isHomepageLoading;
   bool _isOnThisDayLoading = false;
   bool get isOnThisDayLoading => _isOnThisDayLoading;
+  List<LeaderboardEntry> _friendsLeaderboard = [];
+  List<LeaderboardEntry> get friendsLeaderboard => _friendsLeaderboard;
+  bool _isFriendsLeaderboardLoading = false;
+  bool get isFriendsLeaderboardLoading => _isFriendsLeaderboardLoading;
 
   // Notifications
   List<UserNotification> _notifications = [];

lib/services/data_service/data_service_stats.dart

@@ -25,4 +25,38 @@ extension DataServiceStats on DataService {
       _notifyAsync();
     }
   }
+
+  Future<void> fetchFriendsLeaderboard() async {
+    if (_isFriendsLeaderboardLoading) return;
+    _isFriendsLeaderboardLoading = true;
+    _notifyAsync();
+    try {
+      final json = await api.get('/stats/leaderboard/friends');
+      List<dynamic>? list;
+      if (json is List) {
+        list = json;
+      } else if (json is Map) {
+        for (final key in ['leaderboard', 'data', 'items', 'results']) {
+          final value = json[key];
+          if (value is List) {
+            list = value;
+            break;
+          }
+        }
+      }
+      _friendsLeaderboard = list
+              ?.whereType<Map>()
+              .map((e) => LeaderboardEntry.fromJson(
+                    e.map((k, v) => MapEntry(k.toString(), v)),
+                  ))
+              .toList() ??
+          const [];
+    } catch (e) {
+      debugPrint('Failed to fetch friends leaderboard: $e');
+      _friendsLeaderboard = [];
+    } finally {
+      _isFriendsLeaderboardLoading = false;
+      _notifyAsync();
+    }
+  }
 }