Add Flutter project skeleton (Android-only MVP)

Five-layer architecture per DMC_Architektur_und_Design.md: FlightControllerLink
abstraction (Mock + MSP stub), protocol-neutral mission domain layer, App-Mode
state machine with Ready-to-Fly gate, Drift persistence schema, and placeholder
UI screens wired via go_router. App icon generated from design/Y2_pink_dark.svg.
Verified with flutter analyze and flutter test.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/test/widget_test.dart

@@ -0,0 +1,22 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_bloc/flutter_bloc.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:dmc_app/app_mode/app_mode_cubit.dart';
+import 'package:dmc_app/ui/app_shell.dart';
+
+void main() {
+  testWidgets('AppShell zeigt Plan-Screen im Startzustand', (tester) async {
+    await tester.pumpWidget(
+      ProviderScope(
+        child: BlocProvider(
+          create: (_) => AppModeCubit(),
+          child: const MaterialApp(home: AppShell()),
+        ),
+      ),
+    );
+
+    expect(find.text('Plan'), findsOneWidget);
+  });
+}