feat: add ClickHouse schema initializer with agent_metrics DDL

Adds ClickHouseSchemaInitializer that runs on ApplicationReadyEvent,
scanning classpath:clickhouse/*.sql in filename order and executing each
statement. Adds V1__agent_metrics.sql with MergeTree table, tenant/agent
partitioning, and 365-day TTL.

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

cameleer3-server-app/src/main/resources/clickhouse/V1__agent_metrics.sql

@@ -0,0 +1,14 @@
+CREATE TABLE IF NOT EXISTS agent_metrics (
+    tenant_id          LowCardinality(String) DEFAULT 'default',
+    collected_at       DateTime64(3),
+    agent_id           LowCardinality(String),
+    metric_name        LowCardinality(String),
+    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, agent_id, metric_name, collected_at)
+TTL collected_at + INTERVAL 365 DAY DELETE
+SETTINGS index_granularity = 8192;