fix: use statsForApp when application is set without routeId

The stats endpoint was calling statsForRoute(null, agentIds) when
only application was set — this filtered by route_id=null, returning
zero results. Now correctly routes to statsForApp/timeseriesForApp
which queries the stats_1m_app continuous aggregate by application_name.

Also reverts the group parameter alias workaround — the deployed
backend correctly accepts 'application'.

Three code paths now:
- No filters → stats_1m_all (global)
- application only → stats_1m_app (per-app)
- routeId (±application) → stats_1m_route (per-route)

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

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

@@ -28,6 +28,10 @@ public class SearchService {
         return statsStore.stats(from, to);
     }
 
+    public ExecutionStats statsForApp(Instant from, Instant to, String applicationName) {
+        return statsStore.statsForApp(from, to, applicationName);
+    }
+
     public ExecutionStats stats(Instant from, Instant to, String routeId, List<String> agentIds) {
         return statsStore.statsForRoute(from, to, routeId, agentIds);
     }
@@ -36,6 +40,10 @@ public class SearchService {
         return statsStore.timeseries(from, to, bucketCount);
     }
 
+    public StatsTimeseries timeseriesForApp(Instant from, Instant to, int bucketCount, String applicationName) {
+        return statsStore.timeseriesForApp(from, to, bucketCount, applicationName);
+    }
+
     public StatsTimeseries timeseries(Instant from, Instant to, int bucketCount,
                                        String routeId, List<String> agentIds) {
         return statsStore.timeseriesForRoute(from, to, bucketCount, routeId, agentIds);