Feature: Implement AppShell with navigation, add Dashboard, Budget, and Settings views, and integrate GoRouter for routing

finlog_app/app/lib/modules/dashboard/dashboard_view.dart

@@ -0,0 +1,10 @@
+import 'package:flutter/material.dart';
+
+class DashboardView extends StatelessWidget {
+  const DashboardView({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return const Center(child: Text('Dashboard – Willkommen bei Finlog'));
+  }
+}