Flutter code restructuring

pi/ui/lib/app_root.dart

@@ -0,0 +1,52 @@
+import 'package:flutter/material.dart';
+
+import 'screens/splash_screen.dart';
+import 'screens/dashboard_screen.dart';
+
+/// Root widget that manages app state transitions
+class AppRoot extends StatefulWidget {
+  const AppRoot({super.key});
+
+  @override
+  State<AppRoot> createState() => _AppRootState();
+}
+
+class _AppRootState extends State<AppRoot> {
+  bool _initialized = false;
+  String _initStatus = 'Starting...';
+
+  @override
+  void initState() {
+    super.initState();
+    _runInitSequence();
+  }
+
+  Future<void> _runInitSequence() async {
+    // Simulate init checks - replace with real checks later
+    // (UART, GPS, sensors, etc.)
+
+    setState(() => _initStatus = 'Checking systems...');
+    await Future.delayed(const Duration(milliseconds: 800));
+
+    setState(() => _initStatus = 'UART: standby');
+    await Future.delayed(const Duration(milliseconds: 400));
+
+    setState(() => _initStatus = 'GPS: standby');
+    await Future.delayed(const Duration(milliseconds: 400));
+
+    setState(() => _initStatus = 'Ready');
+    await Future.delayed(const Duration(milliseconds: 300));
+
+    setState(() => _initialized = true);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return AnimatedSwitcher(
+      duration: const Duration(milliseconds: 500),
+      child: _initialized
+          ? const DashboardScreen(key: ValueKey('dashboard'))
+          : SplashScreen(key: const ValueKey('splash'), status: _initStatus),
+    );
+  }
+}