remove gateways views

We no longer want to show specific gateway views, this pretty much means removing the `Meshes > Gateways` tab (see below), but there may be the odd other detail we can remove (potentially in the Dataplane Traffic viz)

<img width="1537" height="1209" alt="Image" src="https://github.com/user-attachments/assets/8941409e-2656-4da1-846d-86f30a337509" />