Model Silhouette is wrong when silhouette alpha is not 1

### What happened?

Reported on the forum: https://community.cesium.com/t/behavior-of-entity-model-silhouette-color-options-with-alpha/37082

It seems this may have started happening in version 1.121

https://github.com/user-attachments/assets/d2df426e-ec4e-4637-98e3-4e0ef25d2a9c

It looks like something about the model is not getting translated correctly when it's rotated while processing the silhouette color. Could this be related to https://github.com/CesiumGS/cesium/issues/11067?

### Reproduction steps

1. Load the [3D Models Coloring](https://sandcastle.cesium.com/?src=3D%20Models%20Coloring.html) sandcastle
2. Set the model color to white to avoid confusing the colors
3. Change the Silhouette alpha to anything lower than 1

### Sandcastle example

_No response_

### Environment

Browser: Chrome
CesiumJS Version: 1.124
Operating System: Linux

Start with the 3D Models Coloring Sandcastle example in Chrome and reproduce the misplaced silhouette by lowering the silhouette alpha and rotating the model. Compare the behavior with the related issue #11067 and trace the model silhouette rendering path; done means the silhouette remains correctly positioned for alpha values below 1.

Written by the indexing model from the issue text.