- Extract IWizardDraftRepository interface for testability (NSubstitute cannot
mock sealed classes; the codebase uses fake-style doubles instead).
- Add step-transition, pool-slot, validation, cancel/back, and render-shape tests
using FakeWizardDraftRepository and FakeWizardMessenger.
- Fix wizard payload persistence bug: HandleCallbackAsync and HandleTextAsync
now call SavePayload after ApplyChoice/ApplyText mutations, so subsequent
LoadPayload calls see the user's progress. Previously, local WizardPayload
mutations were discarded and the wizard reset on every step.
- CommitCurrentPoolSlot now auto-creates a slot via EnsureCurrentPoolSlot when
one is missing, so the PoolSlotCapacity → waitlist click is recoverable
even if the user lands on the step without a slot.
