Replace RewardGrantService + ICurrencySpendService + IViewerEntitlements with
IInventoryService. tx.IsFreeplay replaces FakeEntitlements.IsFreeplay; debit
helpers take IInventoryTransaction. ComputePostStateRewardList deleted (replaced
by result.RewardList from CommitAsync). Update 5 test files to new 8-arg ctor.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>