SigilIdentityModule

Binds the default SigilIdentityProvider implementation (Ed25519PrfSigilProvider) into the Hilt graph.

Why a separate @Module (not just a @Provides next door): @Binds abstract members require an abstract class/interface owner, while the existing IdentityModule is an object of @Provides factories. Splitting into two modules at the same install scope is Hilt's idiomatic way to mix both styles without rewriting the existing surface.

Apps that want a different SigilIdentityProvider (e.g. a future zk-passport implementation, midnightOS-Passkeys interop, a fake for tests) replace this module via Hilt's @UninstallModules + @InstallIn(SingletonComponent::class) pattern.