refactor: remove SocialQueryPort — replaced by SocialQuery + FederationAdminQuery

-319 lines. Legacy SocialQueryPort trait, NoopSocialQueryPort,
PanicSocialQueryPort all deleted. Federation repos now implement
FederationAdminQuery (single method). get_users uses FederationAdminQuery.
All other consumers use unified SocialQuery.

crates/adapters/activitypub/src/social_adapter.rs

@@ -275,10 +275,4 @@ impl SocialQuery for CompositeSocialAdapter {
             .map_err(ap_err)?;
         Ok(actors.into_iter().map(|a| a.url).collect())
     }
-
-    async fn list_all_followed_remote_actors(
-        &self,
-    ) -> Result<Vec<domain::models::RemoteActorInfo>, DomainError> {
-        Ok(vec![])
-    }
 }