feat: enable Prometheus metrics for ClickHouse and tenant servers

ClickHouse: enable built-in Prometheus exporter at :9363/metrics via
config.d/prometheus.xml with metrics, events, and async_metrics.
Docker labels added for docker_sd_configs auto-discovery.

Tenant servers: add prometheus.scrape/path/port labels to provisioned
server containers pointing to /api/v1/prometheus:8081.

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

docker-compose.yml

@@ -202,11 +202,16 @@ services:
       - chdata:/var/lib/clickhouse
       - ./docker/clickhouse-init.sql:/docker-entrypoint-initdb.d/init.sql:ro
       - ./docker/clickhouse-users.xml:/etc/clickhouse-server/users.d/default-user.xml
+      - ./docker/clickhouse-config.xml:/etc/clickhouse-server/config.d/prometheus.xml:ro
     healthcheck:
       test: ["CMD-SHELL", "clickhouse-client --password ${CLICKHOUSE_PASSWORD:-cameleer_ch} --query 'SELECT 1'"]
       interval: 10s
       timeout: 5s
       retries: 3
+    labels:
+      - prometheus.scrape=true
+      - prometheus.path=/metrics
+      - prometheus.port=9363
     networks:
       - cameleer