General issues

[adnsawas]

1. It is better to enable null-safety
2. It is better to keep all constant values in separate files. For example put them in files like this:
   • constants/API endpoints
   • constants/Colors
   • constants/Route names

Notes:

• Great idea in including routeName as a static variable inside a screen widget. To me, I like grouping all route names in one file.
• Good job in toggling the home route in MaterialApp using Consumer and auth.isAuth value. This is much better than explicitly navigating to ProfilePage using Navigator.