Add clarifying comment for event transition logic

Co-authored-by: rezwana-karim <126201034+rezwana-karim@users.noreply.github.com>

Author: Copilot

client/src/components/Countdown.tsx

@@ -77,6 +77,7 @@ export default function Countdown({ className = '' }: CountdownProps) {
       const difference = target - now;
 
       if (difference <= 0) {
+        // Event just passed, will find next event on next tick
         setTimeLeft({ days: 0, hours: 0, minutes: 0, seconds: 0 });
         return;
       }