PostgreSQL backend aggregator. One config knob for users:

{repo, [
    {backend, kura_backend_postgres},
    {host, "localhost"},
    {database, "myapp"},
    {pool_size, 10}
]}.

The aggregator wires up:

• pool_module -> kura_pool_minato
• driver_module -> kura_driver_minato
• dialect -> kura_dialect_pg
• capabilities -> declared on kura_pool_minato

kura_pool_pgo and kura_driver_pgo are still here and still work; a repo that wants them says so with pool_module and driver_module of its own.