fix: batchDeleteGroups should ungroup (rename to Unassigned), not hard delete

Changed from apiCall('delete_trace', ...) to updateTraceProfileGroup(name='Unassigned').
This preserves all trace data and just removes the group assignment.
Traces move back to Pending Faces instead of being deleted.

src/views/PeopleView.vue

@@ -1698,39 +1698,33 @@ async function batchDeleteGroups() {
     allTraceIds.push(...(g.trace_ids || []))
   }
   
-  if (!confirm(`Delete ${groupsToDelete.length} group(s) with ${totalTraces} trace(s)?`)) return
+  if (!confirm(`Ungroup ${groupsToDelete.length} group(s) with ${totalTraces} trace(s)?\n\nTraces will be renamed to "Unassigned", not deleted.`)) return
   
   operationLoading.value = true
-  operationMessage.value = `Deleting ${totalTraces} trace(s)...`
+  operationMessage.value = `Ungrouping ${totalTraces} trace(s)...`
   
-  lastDeletedTraces.value = []
   for (const g of groupsToDelete) {
     const traceIds = g.trace_ids || []
-    for (const tid of traceIds) {
-      const trace = clusterTracesMap.value[String(tid)]
-      const fileUuid = trace?.file_uuid
-      console.log('[batchDeleteGroups] trace_id:', tid, 'trace:', trace, 'fileUuid:', fileUuid)
-      if (!fileUuid) {
-        console.error('[batchDeleteGroups] Missing file_uuid for trace:', tid)
-        continue
-      }
-      try {
-        await apiCall('delete_trace', { file_uuid: fileUuid, trace_id: tid })
-        lastDeletedTraces.value.push({ file_uuid: fileUuid, trace_id: tid })
-        console.log('[batchDeleteGroups] Deleted trace:', tid)
-      } catch (e) {
-        console.error('Delete trace failed:', tid, e)
-      }
+    if (!traceIds.length) continue
+    const fileUuid = g.rep_trace?.file_uuid || selectedFileUuid.value
+    if (!fileUuid) continue
+    try {
+      await updateTraceProfileGroup(fileUuid, traceIds, { name: 'Unassigned' })
+    } catch (e) {
+      console.error('Ungroup failed:', g.name, e)
     }
   }
   
-  removeTracesFromClusterCache(allTraceIds)
+  // Remove ungrouped traces from cluster cache so they show in Pending Faces
+  for (const tid of allTraceIds) {
+    delete clusterTracesMap.value[String(tid)]
+  }
   
   operationLoading.value = false
   operationMessage.value = ''
   
   clearSelection()
-  showUndoBannerWithTimer()
+  await loadClusterResults()
 }
 
 async function batchMergeGroups() {