fix: limit event score selection to challenge songs

src/routes/combination/+page.svelte

@@ -249,10 +249,12 @@
     };
   }
 
-  $: charts = releasedSongCharts(allCharts, releaseNow);
   $: currentEvent = eventMode
     ? activeEventAt(events, releaseNow)
     : null;
+  $: charts = releasedSongCharts(allCharts, releaseNow).filter((chart) =>
+    !eventScoreMode || Object.hasOwn(currentEvent?.challengeSongBonusCardIds ?? {}, chart.songId)
+  );
   $: eligibleCards = eventMode
     ? eventOptimizationCardCandidates(allCards, currentEvent)
     : fiveStarCards;