Refit the payment layer onto kessai and orchestra_payment

Problem/Motivation

yoyaku_payment carries its own copy of a generic payment engine: a payment entity, a gateway plugin type, a payment state machine, payment events, and worldline/simulator/audit/views gateways. That generic engine now lives in its own project, kessai, and the "take a payment as a workflow step" glue lives in orchestra's orchestra_payment submodule. yoyaku should consume those rather than duplicate them.

Proposed resolution

Remove the duplicated generic stack from yoyaku_payment and keep only the booking-specific logic, rewritten to call kessai directly.

• Delete the payment entity, the gateway plugin type and ManualGateway, the payment events, the generic PaymentManager, and the yoyaku_payment_worldline/simulator/audit/views submodules (kessai ships kessai_worldline, kessai_simulator, kessai_audit_trail and kessai_views).
• Keep PaymentPolicy and PaymentPolicyResolver (booking pricing, gaining amountDueForOrder), the order-to-gateway resolver, the deposit/no-show field injection, and DefaultSettlementSubscriber, now reacting to kessai's payment events and resolving the order from the payment subject (the yoyaku_transaction).
• Replace the orchestra glue (BookingPaymentInteraction, PaymentWorkflowBridge, StoredCardCleanup, PaymentOrchestraHooks) with a BookingPayableResolver plugin (payable resolver id yoyaku_booking) feeding orchestra_payment's generic payment interaction, and rebuild the deposit/no-show workflow actions on kessai's PaymentManager.

None of these modules have released users, so there is no upgrade path: config and tests are updated in place.

Remaining tasks

• Implement and review.