build(android): update NDK version and set app environment to demo

- Update NDK version in android/app/build.gradle.kts
- Change app environment to demo in lib/main.dart

Author: fulleni

android/app/build.gradle.kts

@@ -11,7 +11,7 @@ plugins {
 android {
     namespace = "com.example.flutter_news_app_mobile_client_full_source_code"
     compileSdk = flutter.compileSdkVersion
-    ndkVersion = "29.0.13113456"
+    ndkVersion = "29.0.13846066"
 
     compileOptions {
         sourceCompatibility = JavaVersion.VERSION_11

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) {