fix: leaderboard empty on first open — decouple from loadAll()

- Add isLeaderboardLoading flag separate from isLoading
- Add loadLeaderboard() method that fires independently of loadAll TTL
- Remove leaderboard from loadAll() Future.wait (failures in dashboard/shop
  no longer silently zero-out leaderboard data)
- setDistrict / setTimePeriod now use isLeaderboardLoading
- contribute_screen calls loadLeaderboard() alongside loadAll() on mount

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/features/gamification/providers/gamification_provider.dart

@@ -22,6 +22,7 @@ class GamificationProvider extends ChangeNotifier {
   String leaderboardTimePeriod = 'all_time'; // 'all_time' | 'this_month'
 
   bool isLoading = false;
+  bool isLeaderboardLoading = false;
   String? error;
 
   // TTL guard — prevents redundant API calls from multiple screens
@@ -44,7 +45,6 @@ class GamificationProvider extends ChangeNotifier {
     try {
       final results = await Future.wait([
         _service.getDashboard(),
-        _service.getLeaderboard(district: leaderboardDistrict, timePeriod: leaderboardTimePeriod),
         _service.getShopItems(),
         _service.getAchievements(),
       ]);
@@ -53,16 +53,11 @@ class GamificationProvider extends ChangeNotifier {
       profile = dashboard.profile;
       submissions = dashboard.submissions;
 
-      final lbResponse = results[1] as LeaderboardResponse;
-      leaderboard = lbResponse.entries;
-      currentUserStats = lbResponse.currentUser;
-      totalParticipants = lbResponse.totalParticipants;
-
-      shopItems = results[2] as List<ShopItem>;
+      shopItems = results[1] as List<ShopItem>;
 
       // Prefer achievements from dashboard API; fall back to fetched or existing defaults
       final dashAchievements = dashboard.achievements;
-      final fetchedAchievements = results[3] as List<AchievementBadge>;
+      final fetchedAchievements = results[2] as List<AchievementBadge>;
 
       if (dashAchievements.isNotEmpty) {
         achievements = dashAchievements;
@@ -80,12 +75,35 @@ class GamificationProvider extends ChangeNotifier {
     }
   }
 
+  // ---------------------------------------------------------------------------
+  // Load leaderboard independently (decoupled from loadAll)
+  // ---------------------------------------------------------------------------
+  Future<void> loadLeaderboard() async {
+    isLeaderboardLoading = true;
+    notifyListeners();
+    try {
+      final response = await _service.getLeaderboard(
+        district: leaderboardDistrict,
+        timePeriod: leaderboardTimePeriod,
+      );
+      leaderboard = response.entries;
+      currentUserStats = response.currentUser;
+      totalParticipants = response.totalParticipants;
+    } catch (e) {
+      error = userFriendlyError(e);
+    } finally {
+      isLeaderboardLoading = false;
+      notifyListeners();
+    }
+  }
+
   // ---------------------------------------------------------------------------
   // Change district filter
   // ---------------------------------------------------------------------------
   Future<void> setDistrict(String district) async {
     if (leaderboardDistrict == district) return;
     leaderboardDistrict = district;
+    isLeaderboardLoading = true;
     notifyListeners();
     try {
       final response = await _service.getLeaderboard(district: district, timePeriod: leaderboardTimePeriod);
@@ -94,6 +112,8 @@ class GamificationProvider extends ChangeNotifier {
       totalParticipants = response.totalParticipants;
     } catch (e) {
       error = userFriendlyError(e);
+    } finally {
+      isLeaderboardLoading = false;
     }
     notifyListeners();
   }
@@ -104,6 +124,7 @@ class GamificationProvider extends ChangeNotifier {
   Future<void> setTimePeriod(String period) async {
     if (leaderboardTimePeriod == period) return;
     leaderboardTimePeriod = period;
+    isLeaderboardLoading = true;
     notifyListeners();
     try {
       final response = await _service.getLeaderboard(district: leaderboardDistrict, timePeriod: period);
@@ -112,6 +133,8 @@ class GamificationProvider extends ChangeNotifier {
       totalParticipants = response.totalParticipants;
     } catch (e) {
       error = userFriendlyError(e);
+    } finally {
+      isLeaderboardLoading = false;
     }
     notifyListeners();
   }

lib/screens/contribute_screen.dart

@@ -104,7 +104,9 @@ class _ContributeScreenState extends State<ContributeScreen>
     super.initState();
     PostHogService.instance.screen('Contribute');
     WidgetsBinding.instance.addPostFrameCallback((_) {
-      context.read<GamificationProvider>().loadAll();
+      final p = context.read<GamificationProvider>();
+      p.loadAll();
+      p.loadLeaderboard(); // independent — always fires regardless of loadAll TTL
     });
   }
 
@@ -274,7 +276,7 @@ class _ContributeScreenState extends State<ContributeScreen>
         const SizedBox(height: 16),
 
         // Leaderboard List
-        if (provider.isLoading && leaderboard.isEmpty)
+        if (provider.isLeaderboardLoading && leaderboard.isEmpty)
           const Padding(
             padding: EdgeInsets.symmetric(vertical: 60),
             child: Center(child: CircularProgressIndicator(strokeWidth: 2)),