fix: pause leaderboard polling when tab is hidden using Page Visibili…

frontend/leaderboard.html

@@ -187,7 +187,27 @@ <h1 class="page-title">Leaderboard</h1>
         setupPaginationListeners();
         fetchLeaderboardData();
         // Poll every 2 minutes to detect new syncs
-        setInterval(fetchLeaderboardData, 2 * 60 * 1000);
+        // Page Visibility API — pause polling when tab is hidden
+        let pollInterval;
+
+        function startPolling() {
+          pollInterval = setInterval(fetchLeaderboardData, 2 * 60 * 1000);
+        }
+
+        function stopPolling() {
+          clearInterval(pollInterval);
+        }
+
+        document.addEventListener("visibilitychange", () => {
+          if (document.visibilityState === "visible") {
+            fetchLeaderboardData(); // immediate refresh when tab becomes visible
+            startPolling();
+          } else {
+            stopPolling();
+          }
+        });
+
+        startPolling();
       });
 
       const leaderboardData = {};