Fix Firebase initialization error - no-app exception

- Add Firebase.initializeApp() call in mainCommon.dart before any Firebase-dependent code
- Make mainCommon() async to support await Firebase.initializeApp()
- Update mainDev.dart to properly await mainCommon() call
- Add android:enableOnBackInvokedCallback='true' to AndroidManifest.xml to fix OnBackInvokedCallback warning

This resolves the 'No Firebase App [DEFAULT] has been created' error that was occurring when firebase_messaging tried to access FirebaseMessaging.instance in homePage.dart. Firebase must be initialized before any Firebase APIs are used.

lib/mainDev.dart

@@ -24,5 +24,5 @@ void main() async {
       logRedux == LogLevel.actions ? [] : [createLoggingMiddleware()];
 
   // In development, Sentry is disabled, so we skip initialization
-  mainCommon(devMiddlewares);
+  await mainCommon(devMiddlewares);
 }