Pivot: skip inspector query when no group_by hierarchy is active

Without group_by there are no coordinate filters, so the view query
would return the full dataset and hang. Early-return on click if
config.group_by is empty.

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

ui/src/pages/Pivot.jsx

@@ -150,6 +150,12 @@ export default function Pivot({ source }) {
           if (!row) return
           const eventFilters = (detail.config || {}).filter || []
           const config = await viewer.save()
+
+          // Without a group_by hierarchy there are no coordinate filters, so the
+          // query would return the entire dataset — skip the inspector in that case
+          const hasHierarchy = (config.group_by || []).length > 0
+          if (!hasHierarchy) return
+
           setClickDetail({ row, config, column_names, eventFilters })
 
           // Use a Perspective view with the event filters + expressions so computed