Move failed count and avg duration from page-derived to backend stats

All stat card values now come from the /search/stats endpoint which
queries the full time window, not just the current page of results.
Consolidated into a single ClickHouse query for efficiency.

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

cameleer3-server-app/src/main/java/com/cameleer3/server/app/search/ClickHouseSearchEngine.java

@@ -89,16 +89,18 @@ public class ClickHouseSearchEngine implements SearchEngine {
 
     @Override
     public ExecutionStats stats(Instant from, Instant to) {
-        Long p99 = jdbcTemplate.queryForObject(
-                "SELECT toInt64(quantile(0.99)(duration_ms)) FROM route_executions " +
-                "WHERE start_time >= ? AND start_time <= ?",
-                Long.class, Timestamp.from(from), Timestamp.from(to));
-        Long active = jdbcTemplate.queryForObject(
-                "SELECT count() FROM route_executions WHERE status = 'RUNNING'",
-                Long.class);
-        return new ExecutionStats(
-                p99 != null ? p99 : 0L,
-                active != null ? active : 0L);
+        return jdbcTemplate.queryForObject(
+                "SELECT countIf(status = 'FAILED') AS failed_count, " +
+                "toInt64(avg(duration_ms)) AS avg_duration_ms, " +
+                "toInt64(quantile(0.99)(duration_ms)) AS p99_duration_ms, " +
+                "countIf(status = 'RUNNING') AS active_count " +
+                "FROM route_executions WHERE start_time >= ? AND start_time <= ?",
+                (rs, rowNum) -> new ExecutionStats(
+                        rs.getLong("failed_count"),
+                        rs.getLong("avg_duration_ms"),
+                        rs.getLong("p99_duration_ms"),
+                        rs.getLong("active_count")),
+                Timestamp.from(from), Timestamp.from(to));
     }
 
     @Override