Supervises the push delivery processes: the Goth worker (FCM OAuth) and the two Pigeon dispatchers.

Children are built from config, so with nothing configured (or with PUSH_ADAPTER=log) this supervises nothing and every delivery routes to the Log provider. Its own restart budget also isolates the app: a dispatcher that somehow crash-loops exhausts this supervisor, provider configured?/0 checks start returning false, and push degrades to Log while the rest of the server runs on.