fix: drop stale instance_id filter from search and scope route stats by app

The exchange search silently filtered by the in-memory agent registry's
current instance IDs on top of application_id. Historical exchanges written
by previous agent instances (or any instance not currently registered, e.g.
after a server restart before agents heartbeat back) were hidden from
results even though they matched the application filter.

Fix: drop the applicationId -> instanceIds resolution in SearchController.
Rely on application_id = ? in ClickHouseSearchIndex; keep explicit
instanceIds filtering only when a client passes them.

Related cleanup: the agentIds parameter on StatsStore.statsForRoute /
timeseriesForRoute was silently discarded inside ClickHouseStatsStore, so
per-route stats aggregated across any apps sharing a routeId. Replace with
String applicationId and add application_id to the stats_1m_route filters
so per-route stats are correctly scoped.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.claude/rules/core-classes.md

@@ -43,7 +43,7 @@ paths:
 
 ## search/ — Execution search and stats
 
-- `SearchService` — search, count, stats, statsForApp, timeseries, timeseriesForApp, timeseriesForRoute, timeseriesGroupedByApp, timeseriesGroupedByRoute, slaCompliance, slaCountsByApp, slaCountsByRoute, topErrors, activeErrorTypes, punchcard, distinctAttributeKeys
+- `SearchService` — search, count, stats, statsForApp, statsForRoute, timeseries, timeseriesForApp, timeseriesForRoute, timeseriesGroupedByApp, timeseriesGroupedByRoute, slaCompliance, slaCountsByApp, slaCountsByRoute, topErrors, activeErrorTypes, punchcard, distinctAttributeKeys. `statsForRoute`/`timeseriesForRoute` take `(routeId, applicationId)` — app filter is applied to `stats_1m_route`.
 - `SearchRequest` / `SearchResult` — search DTOs
 - `ExecutionStats`, `ExecutionSummary` — stats aggregation records
 - `StatsTimeseries`, `TopError` — timeseries and error DTOs