AppDataBackupModule

Optional binding for AppDataBackupProvider.

@BindsOptionalOf declares that a binding of the interface may exist downstream, without actually providing one here. Apps that implement the interface provide a concrete @Provides AppDataBackupProvider elsewhere in their Hilt graph; apps that don't (e.g. BBoard) get an empty Optional injected.

Consumers — currently only com.midnight.kuira.dapp.sigil.SigilPanelViewModel — inject Optional<AppDataBackupProvider> and treat absence as "no app-data round-trip needed" (the previous behavior).

The module is abstract because @BindsOptionalOf only works on abstract methods inside abstract classes / interfaces.