Add firebaseMessagingClient to ensure the Firebase app is created from VITE_FIREBASE_*,
wire PushNotifications (listeners, requestPermissions, register) before token work,
and call getMessaging/getToken/onMessage when firebase/messaging is supported. Hook
startup from main.capacitor and set PushNotifications presentationOptions in
capacitor.config. Depend on firebase and @capacitor/push-notifications.