- Add MultiPoolService: registry of named Sequelize pools with create/get/close/healthcheck
- Add multi-pool config: write host + read replica host with separate ports
- Add DB_CONNECTION_STRING and DB_READ_HOST/DB_READ_PORT env vars
- Add docker-compose.ha.yml: Patroni + etcd cluster, HAProxy, PgBouncer
- Add HAProxy config: routes 5432 (write/primary) / 5433 (read/replica)
- Add PgBouncer userlist template
- Update dev/prod/staging configs with multi-pool hosts
Co-authored-by: Cursor <cursoragent@cursor.com>