Fix ClickHouse OOM during Proxmox nightly backups

Increase ClickHouse memory limit from 1Gi to 2Gi and reduce default
batch size from 5000 to 500. During VM backup snapshots, I/O contention
prevents ClickHouse from flushing writes fast enough, causing buffer
accumulation that exceeds the 1Gi container limit.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

deploy/clickhouse.yaml

@@ -37,7 +37,7 @@ spec:
               memory: "512Mi"
               cpu: "200m"
             limits:
-              memory: "1Gi"
+              memory: "2Gi"
               cpu: "1000m"
   volumeClaimTemplates:
     - metadata: