feat: comprehensive ClickHouse low-memory tuning and switch all storage to ClickHouse

Replace partial memory config with full Altinity low-memory guide
settings. Revert container limit from 6Gi back to 4Gi — proper
tuning (mlock=false, reduced caches/pools/threads, disk spill for
aggregations) makes the original budget sufficient.

Switch all storage feature flags to ClickHouse:
- CAMELEER_STORAGE_SEARCH: opensearch → clickhouse
- CAMELEER_STORAGE_METRICS: postgres → clickhouse
- CAMELEER_STORAGE_STATS: already clickhouse

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

deploy/base/server.yaml

@@ -90,9 +90,9 @@ spec:
                   name: clickhouse-credentials
                   key: CLICKHOUSE_PASSWORD
             - name: CAMELEER_STORAGE_METRICS
-              value: "postgres"
+              value: "clickhouse"
             - name: CAMELEER_STORAGE_SEARCH
-              value: "opensearch"
+              value: "clickhouse"
             - name: CAMELEER_STORAGE_STATS
               value: "clickhouse"