feat: Implement initial authentication, multi-environment support, and core app infrastructure.

lib/routing/app_router.dart

@@ -0,0 +1,22 @@
+import 'package:flutter/material.dart';
+import 'package:go_router/go_router.dart';
+import 'package:real_estate_mobile/features/auth/presentation/screens/login_screen.dart';
+import 'package:real_estate_mobile/features/auth/presentation/screens/signup_screen.dart';
+
+class AppRouter {
+  AppRouter._();
+
+  static final GoRouter router = GoRouter(
+    initialLocation: '/signup',
+    routes: [
+      GoRoute(
+        path: '/signup',
+        builder: (context, state) => const SignupScreen(),
+      ),
+      GoRoute(
+        path: '/login',
+        builder: (context, state) => const LoginScreen(),
+      ),
+    ],
+  );
+}