Rework top bar to not include toolbar

Closes #7679 by creating a definite top bar, and moving the toolbar
below it. Still side-steps the E2E test issue by allowing the modeling
scene extend under this top bar. I will finally address this in the next
step, which is bringing back a proper sidebar that doesn't overlay the
modeling scene.

I have a fast-follow PR coming that adds visual undo and redo buttons to
this top bar, but I wanted to keep them separate.

src/App.tsx

@@ -71,8 +71,8 @@ import { Toolbar } from '@src/Toolbar'
 sceneInfra.camControls.engineStreamActor = engineStreamActor
 
 maybeWriteToDisk()
-  .then(() => { })
+  .then(() => {})
-  .catch(() => { })
+  .catch(() => {})
 
 export function App() {
   const { state: modelingState } = useModelingContext()