fix: increase ClickHouse pool size and reduce flush interval

Pool was hardcoded to 10 connections serving 7 concurrent write
streams + UI reads, causing "too many simultaneous queries" and
WriteBuffer overflow. Pool now defaults to 50 (configurable via
clickhouse.pool-size), flush interval reduced from 1000ms to 500ms.

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

cameleer3-server-app/src/main/resources/application.yml

@@ -35,7 +35,7 @@ agent-registry:
 ingestion:
   buffer-capacity: 50000
   batch-size: 5000
-  flush-interval-ms: 1000
+  flush-interval-ms: 500
 
 cameleer:
   body-size-limit: ${CAMELEER_BODY_SIZE_LIMIT:16384}