fix: ensure useEffect returns cleanup in TransactionTracker

Author: extolkom

frontend/src/components/TransactionTracker.tsx

@@ -150,14 +150,19 @@ export default function TransactionTracker({
 
   // Reset state when returning to idle
   useEffect(() => {
+    let timer: ReturnType<typeof setTimeout> | undefined;
+
     if (status === "idle") {
-      const timer = setTimeout(() => {
+      timer = setTimeout(() => {
         setPollCount(0);
         setStreamData(null);
         setPreviousStreamData(null);
       }, 0);
-      return () => clearTimeout(timer);
     }
+
+    return () => {
+      if (timer) clearTimeout(timer);
+    };
   }, [status]);
 
   // Render based on status