NotificationChannelSpec
data class NotificationChannelSpec(val id: String, val name: String, val description: String, val importance: Int = NotificationManager.IMPORTANCE_DEFAULT, val vibrate: Boolean = false)
A single notification channel the host app wants created. Kept app-agnostic — the app declares its own channels (ids, names, importance) and passes them to NotificationChannelManager.createChannels; this module owns none of them.
importance is an android.app.NotificationManager.IMPORTANCE_* constant.