[Bug]: Sidebar context menu behaves incorrectly in reffed entrys

[JReinhold]

The new sidebar context menu is shown whenever a test provider addon determines that it should show for a given entry.

Right now that is true for reffed entries as well (stories in composed Storybooks). It shows up, but the invariant fails because the entry couldn't be found in the index:

Export-1732262108608.mp4

There are multiple solutions here:

1. Never show the sidebar context menu in refs, ever. This assumes that addons can't do any meaningful with them, which I don't know if is true.
2. In addon-test specifically, disable the menu entry in refs, because addon-test can't do anything meaningful with them. for this to work in general, we should change the logic to find the entry in the ref as well.