The combo widget still carried a hollow optional input dot on the node edge
because the new frontend adds a widget-linked input socket for every non-
socketless widget. Mark preview_tiny_vae socketless (legacy dict key, same
pattern KJNodes uses in curve_nodes.py) so it renders like the VAE loader's
model-selector dropdown with no dot. Combo still sourced from
models/vae_approx. Align .tests + docs with source.