reorg ui into app

lib/app/screens/root_shell_screen.dart

@@ -0,0 +1,28 @@
+import 'package:flutter/material.dart';
+import 'package:go_router/go_router.dart';
+
+class RootShellScreen extends StatelessWidget {
+  const RootShellScreen({
+    super.key,
+    required this.child,
+  });
+
+  final Widget child;
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      body: child,
+      bottomNavigationBar: BottomAppBar(
+        child: Center(
+          child: TextButton(
+            onPressed: () {
+              context.push('/now-playing');
+            },
+            child: Text('Now playing...'),
+          ),
+        ),
+      ),
+    );
+  }
+}