v0.4.0
Adds createCustomer and detachPaymentMethod to the PaymentGateway contract, completing the stored-customer / saved-method surface so a host app no longer has to reach into a gateway SDK directly for them.
createCustomer(string $account, ?string $email, ?string $name): string— create-or-return the gateway customer, stamping the account key into metadata for reconciliation.detachPaymentMethod(string $account, string $paymentMethodId): void— idempotent detach; a no-op for vault-less gateways.
Implemented in ManualPaymentGateway (deterministic local ref; no-op detach) and the dogfooded FakePaymentGateway. Minor bump: the interface addition is breaking for external implementers. Adapter packages (laravel-billing-stripe, laravel-billing-mollie) implement these in their own v0.4.0.