No feedback to user about running simulations or their ending

I've got a simulation running now. After I clicked "simulate", I think I did get a "running simulation" timer initially, but it seems to have gone now, so I'm back to the screen with the "simulate" button:


There's nothing here to tell me if the simulation has finished (I assume it didn't because the screen changes to the one with plots when that does), or if the simulation has failed. I *think* it's still running---app.log still hasn't got anything after this:

```
2023-07-13 16:38:20,175|root|DEBUG - ComponentSync disconnecting from simConfig.cvode_active
2023-07-13 16:44:14,958|root|INFO - Scheduling simulation on 1 cores with ...
2023-07-13 16:44:14,963|root|DEBUG - Running single core simulation
```

but there's no way to tell. As a user, I don't know what to do---should I wait more, should I click simulate again, should I start again from scratch?

L’issue ne nomme aucun fichier source ni aucun test. Suivez l’action simulate, son état de minuteur en cours d’exécution, la transition vers les plots et les messages de app.log ; c’est terminé lorsque l’UI distingue clairement les états en cours d’exécution, terminé et échoué, et indique à l’utilisateur quoi faire.

Rédigé par le modèle d'indexation à partir du texte de l'issue.