Populate supported models from registry

So this comes from `SupportedModels` while the `list_models` for RL calls the model registry. Should this come from model registry as well? If the user registers a new model, `list_model` would not include the new model right?

_Originally posted by @digicosmos86 in https://github.com/lnccbrown/HSSM/pull/971#discussion_r3336927856_

Start by tracing SupportedModels and the list_models path used for RL, then compare how each obtains model names from the model registry. Verify the behavior after a user registers a new model; done means the model-listing behavior consistently includes that newly registered model if the registry is intended as the source.

Written by the indexing model from the issue text.