Make stats endpoint respect selected time window instead of hardcoded last hour

P99 latency and active count now use the same from/to parameters as the
timeseries sparklines, so all stat cards are consistent with the user's
selected time range.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/api/queries/executions.ts

@@ -2,14 +2,23 @@ import { useQuery } from '@tanstack/react-query';
 import { api } from '../client';
 import type { SearchRequest } from '../schema';
 
-export function useExecutionStats() {
+export function useExecutionStats(timeFrom: string | undefined, timeTo: string | undefined) {
   return useQuery({
-    queryKey: ['executions', 'stats'],
+    queryKey: ['executions', 'stats', timeFrom, timeTo],
     queryFn: async () => {
-      const { data, error } = await api.GET('/search/stats');
+      const { data, error } = await api.GET('/search/stats', {
+        params: {
+          query: {
+            from: timeFrom!,
+            to: timeTo || undefined,
+          },
+        },
+      });
       if (error) throw new Error('Failed to load stats');
       return data!;
     },
+    enabled: !!timeFrom,
+    placeholderData: (prev) => prev,
     refetchInterval: 10_000,
   });
 }