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>

cameleer3-server-core/src/main/java/com/cameleer3/server/core/search/ExecutionStats.java

@@ -0,0 +1,9 @@
+package com.cameleer3.server.core.search;
+
+/**
+ * Aggregate execution statistics.
+ *
+ * @param p99LatencyMs 99th percentile duration in milliseconds (last hour)
+ * @param activeCount  number of currently running executions
+ */
+public record ExecutionStats(long p99LatencyMs, long activeCount) {}

cameleer3-server-core/src/main/java/com/cameleer3/server/core/search/SearchEngine.java

@@ -24,4 +24,11 @@ public interface SearchEngine {
      * @return total number of matching executions
      */
     long count(SearchRequest request);
+
+    /**
+     * Compute aggregate stats: P99 latency and count of currently running executions.
+     *
+     * @return execution stats
+     */
+    ExecutionStats stats();
 }

cameleer3-server-core/src/main/java/com/cameleer3/server/core/search/SearchService.java

@@ -28,4 +28,11 @@ public class SearchService {
     public long count(SearchRequest request) {
         return engine.count(request);
     }
+
+    /**
+     * Compute aggregate execution stats (P99 latency, active count).
+     */
+    public ExecutionStats stats() {
+        return engine.stats();
+    }
 }