fix: filter exchanges by application and restore snake_case sort columns

Add application_name filter to OpenSearch query builder — sidebar
app selection now correctly filters the exchange list. The
application field was being resolved to agentIds in the controller
but never applied as a query filter in OpenSearch.

Also restore snake_case sort column mapping since the OpenSearch
toMap() serializer uses snake_case field names (start_time, route_id,
etc.), not camelCase.

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

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

@@ -166,6 +166,8 @@ public class OpenSearchIndex implements SearchIndex {
             filter.add(termQuery("agent_id.keyword", request.agentId()));
         if (request.correlationId() != null)
             filter.add(termQuery("correlation_id.keyword", request.correlationId()));
+        if (request.application() != null && !request.application().isBlank())
+            filter.add(termQuery("application_name.keyword", request.application()));
 
         // Full-text search across all fields + nested processor fields
         if (request.text() != null && !request.text().isBlank()) {