Add API integration test suite with Postgres and ClickHouse coverage

tests/api/docker/clickhouse-init/00-create-db.sql

@@ -0,0 +1,3 @@
+-- CLICKHOUSE_DB already creates this before init scripts run; kept as a guard so
+-- db/clickhouse/schema.sql (which hardcodes the `umami.` prefix) never fails.
+CREATE DATABASE IF NOT EXISTS umami;