feat(server): persist server self-metrics into ClickHouse

Snapshot the full Micrometer registry (cameleer business metrics, alerting
metrics, and Spring Boot Actuator defaults) every 60s into a new
server_metrics table so server health survives restarts without an external
Prometheus. Includes a dashboard-builder reference for the SaaS team.

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

cameleer-server-app/src/main/resources/clickhouse/init.sql

@@ -401,6 +401,29 @@ CREATE TABLE IF NOT EXISTS route_catalog (
 ENGINE = ReplacingMergeTree(last_seen)
 ORDER BY (tenant_id, environment, application_id, route_id);
 
+-- ── Server Self-Metrics ────────────────────────────────────────────────
+-- Periodic snapshot of the server's own Micrometer registry (written by
+-- ServerMetricsSnapshotScheduler). No `environment` column — the server
+-- straddles environments. `statistic` distinguishes Timer/DistributionSummary
+-- sub-measurements (count, total_time, max, mean) from plain counter/gauge values.
+
+CREATE TABLE IF NOT EXISTS server_metrics (
+    tenant_id          LowCardinality(String) DEFAULT 'default',
+    collected_at       DateTime64(3),
+    server_instance_id LowCardinality(String),
+    metric_name        LowCardinality(String),
+    metric_type        LowCardinality(String),
+    statistic          LowCardinality(String) DEFAULT 'value',
+    metric_value       Float64,
+    tags               Map(String, String) DEFAULT map(),
+    server_received_at DateTime64(3) DEFAULT now64(3)
+)
+ENGINE = MergeTree()
+PARTITION BY (tenant_id, toYYYYMM(collected_at))
+ORDER BY (tenant_id, collected_at, server_instance_id, metric_name, statistic)
+TTL toDateTime(collected_at) + INTERVAL 90 DAY DELETE
+SETTINGS index_granularity = 8192;
+
 -- insert_id tiebreak for keyset pagination (fixes same-millisecond cursor collision).
 -- IF NOT EXISTS on ADD COLUMN is idempotent. MATERIALIZE COLUMN is a background mutation,
 -- effectively a no-op once all parts are already materialized.