reorg ui into app

lib/app/router.dart

@@ -0,0 +1,40 @@
+import 'package:go_router/go_router.dart';
+
+import 'screens/album_screen.dart';
+import 'screens/artist_screen.dart';
+import 'screens/library_screen.dart';
+import 'screens/now_playing_screen.dart';
+import 'screens/root_shell_screen.dart';
+import 'screens/settings_screen.dart';
+
+final router = GoRouter(
+  routes: [
+    ShellRoute(
+      builder: (context, state, child) => RootShellScreen(child: child),
+      routes: [
+        GoRoute(
+          path: '/',
+          builder: (context, state) => LibraryScreen(),
+          routes: [
+            GoRoute(
+              path: 'album',
+              builder: (context, state) => AlbumScreen(),
+            ),
+            GoRoute(
+              path: 'artist',
+              builder: (context, state) => ArtistScreen(),
+            ),
+          ],
+        ),
+      ],
+    ),
+    GoRoute(
+      path: '/now-playing',
+      builder: (context, state) => NowPlayingScreen(),
+    ),
+    GoRoute(
+      path: '/settings',
+      builder: (context, state) => SettingsScreen(),
+    ),
+  ],
+);