ConsoleUserInteractionGateway
UserInteractionGateway backed by the host console (stdin / stdout).
JVM-only — readlnOrNull() is multiplatform but stdin / stdout are meaningful on JVM/Android-host CLI runs. iOS / Native consumers inject their own platform-appropriate gateway.
The implementation is intentionally trivial: print on tell, prompt and read a line on ask. Both calls block the current thread; that is acceptable for CLI examples but consumers running in non-blocking environments should inject their own gateway.