frotnend: wait until endpoint compatibility is ready

Author: malinskibeniamin

frontend/src/config.ts

@@ -314,6 +314,12 @@ setTimeout(() => {
       return;
     }
 
+    // Don't emit sidebar items until endpoint compatibility is known,
+    // otherwise items gated by feature support will flicker.
+    if (!api.endpointCompatibility) {
+      return;
+    }
+
     const sidebarItems = embeddedAvailableRoutesObservable.routes.map(
       (r, i) =>
         ({