Make engine reconnection test pass every time (#3066)

* Ensure that isFreezeFrame is reset by isFirstRender, because it can't be a freeze frame if it's the first render

* `restart`-type engine starts should count as first renders

* Ensure we don't see a loading spinner after network is reconnected in test

* Make `waitForPageLoad` robust against if the page has already loaded
and make it actually wait for the Start Sketch button to be enabled

---------

Co-authored-by: 49fl <ircsurfer33@gmail.com>

src/hooks/useSetupEngineManager.ts

@@ -45,9 +45,6 @@ export function useSetupEngineManager(
       streamRef?.current?.offsetWidth ?? 0,
       streamRef?.current?.offsetHeight ?? 0
     )
-    if (restart) {
-      kclManager.isFirstRender = false
-    }
     engineCommandManager.start({
       restart,
       setMediaStream: (mediaStream) => setMediaStream(mediaStream),