chore: switch app environment from development to demo

- Changed the appEnvironment constant from AppEnvironment.development to AppEnvironment.demo in the main.dart file.
- This modification affects the application configuration and may impact the data displayed to users.

Author: fulleni

lib/main.dart

@@ -6,7 +6,7 @@ import 'package:flutter_news_app_mobile_client_full_source_code/app/services/spl
 import 'package:flutter_news_app_mobile_client_full_source_code/bootstrap.dart';
 
 // Define the current application environment (production/development/demo).
-const appEnvironment = AppEnvironment.development;
+const appEnvironment = AppEnvironment.demo;
 
 void main() async {
   final appConfig = switch (appEnvironment) {