refactor: remove unused updateClusterAfterMerge function

- No longer needed with new merge_groups API
- merge_groups API handles group merging server-side
- Frontend only needs to refresh data after merge

src/views/PeopleView.vue

@@ -1598,27 +1598,6 @@ function removeTracesFromClusterCache(traceIds: number[]) {
   clusterResultsCache.value[selectedFileUuid.value] = validClusters
 }
 
-function updateClusterAfterMerge(sourceGroupId: string, targetGroupId: string) {
-  const clusters = clusterResultsCache.value[selectedFileUuid.value]
-  if (!clusters) return
-  
-  const sourceCluster = clusters.find((c: any) => c.identity_uuid === sourceGroupId)
-  const targetCluster = clusters.find((c: any) => c.identity_uuid === targetGroupId)
-  
-  if (sourceCluster && targetCluster) {
-    targetCluster.trace_ids = [...targetCluster.trace_ids, ...sourceCluster.trace_ids]
-    targetCluster.trace_count = targetCluster.trace_ids.length
-    
-    const idx = clusters.findIndex((c: any) => c.identity_uuid === sourceGroupId)
-    if (idx >= 0) {
-      clusters.splice(idx, 1)  // Remove empty source group from cache
-    }
-    
-    // Trigger computed property update
-    clusterResultsCache.value = { ...clusterResultsCache.value }
-  }
-}
-
 async function batchDeleteFaces() {
   if (!selectedFaces.value.length) return