Within a thing card, the app list needs to depend on the context

[b1conrad]

When adding the first app to a thing, we choose from a list of all of the apps installed in the Manifold instance.

Once several apps are added to the thing, adding an app still lists all of the apps installed. It should list only apps which are installed in the Manifold instance, but which have not already been added to the thing. It's unclear what would happen if an owner tried adding the same app again.

When requesting deletion of an app from their thing, the owner selects from a list of all apps installed in the Manifold instance. Instead, the list should only include apps that it makes sense to delete, that is, those which are in the thing.