Add division by zero guards in TraceFilter traceList and caseTotalPercent

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

src/components/Discover/Map/Filter/TraceFilter.vue

@@ -175,6 +175,7 @@ const traceCountTotal = computed(() => {
 });
 
 const traceList = computed(() => {
+  if (traceCountTotal.value === 0) return [];
   return baseTraces.value
     .map((trace) => {
       return {
@@ -191,6 +192,7 @@ const traceList = computed(() => {
 });
 
 const caseTotalPercent = computed(() => {
+  if (traceCountTotal.value === 0) return "0%";
   const ratioSum =
     traceList.value
       .map((trace) => trace.base_count)