Issue #3612196: Add a cancellation and refund policy on the resource type

Adds a per-type cancellation/refund policy (allow_self_cancellation, allow_refund, both default off, plus the deadlines) with a per-resource override, resolved by CancellationPolicyResolver. PrepareCancellation writes yoyaku_allow_cancellation / yoyaku_allow_refund; the example workflow's inclusive fork gates the customer cancel branch on the first (so a disabled resource never parks on booking_cancel and gets no cancel link), and CheckRefundableAction folds in the second. Resource + type forms group the fields in a collapsed section. Kernel-tested resolver cascade.