diff --git a/finlog_app/app/lib/app/router.dart b/finlog_app/app/lib/app/router.dart
new file mode 100644
index 0000000..e3ca04c
--- /dev/null
+++ b/finlog_app/app/lib/app/router.dart
@@ -0,0 +1,79 @@
+import 'package:app/features/login/pages/login_page.dart';
+import 'package:app/main.dart';
+import 'package:flutter/material.dart';
+import 'package:go_router/go_router.dart';
+import 'package:animations/animations.dart';
+
+/// Centralized route names and paths.
+/// Splash is not routable (handled before router creation).
+enum AppRoute {
+  login('/login'),
+  home('/home'),
+  inventory('/inventory'),
+  inventoryAdd('/inventory/add'),
+  budget('/budget'),
+  expenses('/expenses');
+
+  const AppRoute(this.path);
+
+  final String path;
+}
+
+/// Generic animated page using the `animations` package.
+/// Change [transitionType] to vertical / scaled globally if desired.
+class AnimatedPage<T> extends CustomTransitionPage<T> {
+  AnimatedPage({
+    required LocalKey super.key,
+    required super.child,
+    Duration duration = const Duration(milliseconds: 400),
+    SharedAxisTransitionType transitionType =
+        SharedAxisTransitionType.horizontal,
+  }) : super(
+         transitionDuration: duration,
+         transitionsBuilder: (context, animation, secondary, child) {
+           return SharedAxisTransition(
+             animation: animation,
+             secondaryAnimation: secondary,
+             transitionType: transitionType,
+             child: child,
+           );
+         },
+       );
+}
+
+/// Helper to create a GoRoute with the global AnimatedPage transition.
+/// Use this for EVERY route to keep transitions consistent.
+GoRoute _r(
+  AppRoute route,
+  Widget Function(BuildContext, GoRouterState) builder, {
+  List<RouteBase> routes = const [],
+  SharedAxisTransitionType transitionType = SharedAxisTransitionType.horizontal,
+}) {
+  return GoRoute(
+    path: route.path,
+    name: route.name,
+    pageBuilder: (context, state) => AnimatedPage<void>(
+      key: state.pageKey,
+      child: builder(context, state),
+      transitionType: transitionType,
+    ),
+    routes: routes,
+  );
+}
+
+/// Builds the application-wide router. The initial route is decided before creation.
+GoRouter buildAppRouter(AppRoute initialRoute) {
+  return GoRouter(
+    initialLocation: initialRoute.path,
+    routes: [
+      _r(AppRoute.login, (ctx, st) => const LoginPage()),
+      _r(AppRoute.home, (ctx, st) => const MyApp()),
+      // Add feature routes here, all getting the same animation:
+      // _r(AppRoute.inventory, (ctx, st) => const InventoryPage(), routes: [
+      //   _r(AppRoute.inventoryAdd, (ctx, st) => const AddItemPage()),
+      // ]),
+      // _r(AppRoute.budget, (ctx, st) => const BudgetPage()),
+      // _r(AppRoute.expenses, (ctx, st) => const ExpensesPage()),
+    ],
+  );
+}
diff --git a/finlog_app/app/lib/app/startup/domain/initialize_app.dart b/finlog_app/app/lib/app/startup/domain/initialize_app.dart
new file mode 100644
index 0000000..13f5666
--- /dev/null
+++ b/finlog_app/app/lib/app/startup/domain/initialize_app.dart
@@ -0,0 +1,12 @@
+import 'package:app/app/router.dart';
+
+class InitializeAppUseCase {
+  Future<AppRoute> call() async {
+    // Beispiel: ggf. weitere Init-Schritte
+    // await _migrateIfNeeded(prefs);
+    // await _warmupCaches();
+
+    // return auth.isLoggedIn ? AppRoute.home : AppRoute.login;
+    return AppRoute.login;
+  }
+}
diff --git a/finlog_app/app/lib/app/theme.dart b/finlog_app/app/lib/app/theme.dart
new file mode 100644
index 0000000..9d054f8
--- /dev/null
+++ b/finlog_app/app/lib/app/theme.dart
@@ -0,0 +1,58 @@
+import 'package:flutter/material.dart';
+import 'package:fluttery/fluttery.dart';
+import 'package:fluttery/preferences.dart';
+
+/// Controls the current theme of the application.
+/// Loads the theme from Preferences or falls back to system default.
+class ThemeController extends ChangeNotifier {
+  final Preferences _prefs;
+
+  // vars
+  ThemeMode _themeMode = ThemeMode.system;
+
+  /// Constructor
+  ThemeController() : _prefs = App.service<Preferences>();
+
+  /// Loads theme from Preferences (or defaults to system).
+  Future<void> init() async {
+    final saved = await _prefs.getString('theme');
+    if (saved == null) {
+      _themeMode = ThemeMode.system;
+    } else {
+      _themeMode = _fromString(saved);
+    }
+    notifyListeners();
+  }
+
+  /// Sets theme and persists it in Preferences.
+  Future<void> setTheme(ThemeMode mode) async {
+    _themeMode = mode;
+    notifyListeners();
+    await _prefs.setString('theme', _toString(mode));
+  }
+
+  ThemeMode _fromString(String value) {
+    switch (value) {
+      case 'light':
+        return ThemeMode.light;
+      case 'dark':
+        return ThemeMode.dark;
+      case 'system':
+      default:
+        return ThemeMode.system;
+    }
+  }
+
+  String _toString(ThemeMode mode) {
+    switch (mode) {
+      case ThemeMode.light:
+        return 'light';
+      case ThemeMode.dark:
+        return 'dark';
+      case ThemeMode.system:
+        return 'system';
+    }
+  }
+
+  ThemeMode get themeMode => _themeMode;
+}
diff --git a/finlog_app/app/lib/features/login/pages/login_page.dart b/finlog_app/app/lib/features/login/pages/login_page.dart
new file mode 100644
index 0000000..1b13ed1
--- /dev/null
+++ b/finlog_app/app/lib/features/login/pages/login_page.dart
@@ -0,0 +1,82 @@
+import 'package:app/app/router.dart';
+import 'package:flutter/material.dart';
+import 'package:go_router/go_router.dart';
+
+class LoginPage extends StatefulWidget {
+  const LoginPage({super.key});
+
+  @override
+  State<LoginPage> createState() => _LoginPageState();
+}
+
+class _LoginPageState extends State<LoginPage> {
+  bool _loading = false;
+
+  Future<void> _simulateLogin() async {
+    if (_loading) return;
+    setState(() => _loading = true);
+
+    // Simulate latency, perform demo login, then go home.
+    await Future<void>.delayed(const Duration(milliseconds: 900));
+    // await App.service<Auth>().login('demo', 'demo');
+
+    if (!mounted) return;
+    context.go(AppRoute.home.path);
+
+    setState(() => _loading = false);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    return Scaffold(
+      appBar: AppBar(title: const Text('Login')),
+      body: Center(
+        child: ConstrainedBox(
+          constraints: const BoxConstraints(maxWidth: 360),
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: [
+              const FlutterLogo(size: 64),
+              const SizedBox(height: 24),
+              Text('Please sign in', style: theme.textTheme.titleMedium),
+              const SizedBox(height: 24),
+              SizedBox(
+                width: double.infinity,
+                child: ElevatedButton(
+                  onPressed: _loading ? null : _simulateLogin,
+                  child: AnimatedSwitcher(
+                    duration: const Duration(milliseconds: 250),
+                    transitionBuilder: (child, anim) =>
+                        FadeTransition(opacity: anim, child: child),
+                    child: _loading
+                        ? const SizedBox(
+                            key: ValueKey('loading'),
+                            width: 20,
+                            height: 20,
+                            child: CircularProgressIndicator(strokeWidth: 2),
+                          )
+                        : const Text('Login', key: ValueKey('text')),
+                  ),
+                ),
+              ),
+              const SizedBox(height: 12),
+              AnimatedSwitcher(
+                duration: const Duration(milliseconds: 250),
+                child: _loading
+                    ? Padding(
+                        padding: const EdgeInsets.only(top: 4),
+                        child: Text(
+                          'Signing you in…',
+                          style: theme.textTheme.bodySmall,
+                        ),
+                      )
+                    : const SizedBox.shrink(),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}
diff --git a/finlog_app/app/lib/main.dart b/finlog_app/app/lib/main.dart
index 8f08deb..9da0093 100644
--- a/finlog_app/app/lib/main.dart
+++ b/finlog_app/app/lib/main.dart
@@ -1,3 +1,6 @@
+import 'package:app/app/router.dart';
+import 'package:app/app/startup/domain/initialize_app.dart';
+import 'package:app/app/theme.dart';
 import 'package:flutter/material.dart';
 import 'package:fluttery/fluttery.dart';
 import 'package:fluttery/logger.dart';
@@ -14,7 +17,25 @@ Future<void> main() async {
   final logger = App.service<Logger>();
   logger.debug("[MAIN] Registered all default services");
 
-  runApp(const MyApp());
+  // Run initialization before building router
+  final init = InitializeAppUseCase();
+  final startRoute = await init();
+
+  final themeController = ThemeController();
+  await themeController.init();
+
+  runApp(
+    AnimatedBuilder(
+      animation: themeController,
+      builder: (context, _) => MaterialApp.router(
+        title: 'App',
+        theme: ThemeData.light(),
+        darkTheme: ThemeData.dark(),
+        themeMode: themeController.themeMode,
+        routerConfig: buildAppRouter(startRoute),
+      ),
+    ),
+  );
 }
 
 class MyApp extends StatelessWidget {
@@ -76,11 +97,7 @@ class _MyHomePageState extends State<MyHomePage> {
               '$_counter',
               style: Theme.of(context).textTheme.headlineMedium,
             ),
-            TextButton(
-              onPressed: () {
-              },
-              child: Text("Print workers"),
-            ),
+            TextButton(onPressed: () {}, child: Text("Print workers")),
           ],
         ),
       ),
diff --git a/finlog_app/app/pubspec.yaml b/finlog_app/app/pubspec.yaml
index 4a153ec..2b162fe 100644
--- a/finlog_app/app/pubspec.yaml
+++ b/finlog_app/app/pubspec.yaml
@@ -37,6 +37,8 @@ dependencies:
   # The following adds the Cupertino Icons font to your application.
   # Use with the CupertinoIcons class for iOS style icons.
   cupertino_icons: ^1.0.8
+  go_router: ^16.2.2
+  animations: ^2.0.11
 
 dev_dependencies:
   flutter_test:
diff --git a/finlog_app/fluttery/test/mocks/mocks.dart b/finlog_app/fluttery/test/mocks/mocks.dart
index 82c20fa..4dca3ec 100644
--- a/finlog_app/fluttery/test/mocks/mocks.dart
+++ b/finlog_app/fluttery/test/mocks/mocks.dart
@@ -1,3 +1,4 @@
+import 'package:flutter/cupertino.dart';
 import 'package:fluttery/logger.dart';
 import 'package:mocktail/mocktail.dart';
 
@@ -8,16 +9,18 @@ class MockUtils {
     final logger = MockLogger();
 
     when(() => logger.debug(any())).thenAnswer((a) {
-      print("[DEBUG] ${a.positionalArguments[0]}");
+      debugPrint("[DEBUG] ${a.positionalArguments[0]}");
     });
     when(() => logger.info(any())).thenAnswer((a) {
-      print("[INFO] ${a.positionalArguments[0]}");
+      debugPrint("[INFO] ${a.positionalArguments[0]}");
     });
     when(() => logger.warning(any())).thenAnswer((a) {
-      print("[WARN] ${a.positionalArguments[0]}");
+      debugPrint("[WARN] ${a.positionalArguments[0]}");
     });
     when(() => logger.error(any(), any(), any())).thenAnswer((a) {
-      print("[ERROR] ${a.positionalArguments[0]}\n${a.positionalArguments[2]}");
+      debugPrint(
+        "[ERROR] ${a.positionalArguments[0]}\n${a.positionalArguments[2]}",
+      );
     });
 
     return logger;