fix: use alias in ORDER BY for processor metrics query

ClickHouse rejects countMerge() in ORDER BY after GROUP BY because the
column is already finalized to UInt64. Use the SELECT alias instead.

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

cameleer3-server-app/src/main/java/com/cameleer3/server/app/controller/RouteMetricsController.java

@@ -164,7 +164,7 @@ public class RouteMetricsController {
             sql.append(" AND application_id = " + lit(appId));
         }
         sql.append(" GROUP BY processor_id, processor_type, route_id, application_id");
-        sql.append(" ORDER BY countMerge(total_count) DESC");
+        sql.append(" ORDER BY total_count DESC");
 
         List<ProcessorMetrics> metrics = jdbc.query(sql.toString(), (rs, rowNum) -> {
             long totalCount = rs.getLong("total_count");