ReceiveTargetStore
The active (network, unshielded address) the background receive poll should check.
Written by MidnightSdkProvider whenever it builds / switches the SDK (it has both the config's network and the wallet address); read by ReceivePollWorker, which runs when the live SDK may be gone (session locked / process backgrounded) and so can't ask it.
Public data (a network name + a Bech32m receive address) — plain prefs, no secret.