Fix status filter OR logic and add P99/active stats endpoint

Status filter now parses comma-separated values into SQL IN clause
instead of exact match, so filtering by multiple statuses works.

Added GET /api/v1/search/stats returning P99 latency (last hour) and
active execution count, wired into the UI stat cards with 10s polling.

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

ui/src/pages/executions/ExecutionExplorer.tsx

@@ -1,4 +1,4 @@
-import { useSearchExecutions } from '../../api/queries/executions';
+import { useSearchExecutions, useExecutionStats } from '../../api/queries/executions';
 import { useExecutionSearch } from './use-execution-search';
 import { StatCard } from '../../components/shared/StatCard';
 import { Pagination } from '../../components/shared/Pagination';
@@ -10,6 +10,7 @@ export function ExecutionExplorer() {
   const { toSearchRequest, offset, limit, setOffset } = useExecutionSearch();
   const searchRequest = toSearchRequest();
   const { data, isLoading, isFetching } = useSearchExecutions(searchRequest);
+  const { data: stats } = useExecutionStats();
 
   const total = data?.total ?? 0;
   const results = data?.data ?? [];
@@ -42,8 +43,8 @@ export function ExecutionExplorer() {
         <StatCard label="Total Matches" value={total.toLocaleString()} accent="amber" change={`from current search`} />
         <StatCard label="Avg Duration" value={`${avgDuration}ms`} accent="cyan" />
         <StatCard label="Failed (page)" value={failedCount.toString()} accent="rose" />
-        <StatCard label="P99 Latency" value="--" accent="green" change="stats endpoint coming soon" />
-        <StatCard label="Active Now" value="--" accent="blue" change="stats endpoint coming soon" />
+        <StatCard label="P99 Latency" value={stats ? `${stats.p99LatencyMs}ms` : '--'} accent="green" change="last hour" />
+        <StatCard label="Active Now" value={stats ? stats.activeCount.toString() : '--'} accent="blue" change="running executions" />
       </div>
 
       {/* Filters */}