feat(task-0003): implement boot flow service with menu restart signal and state transitions

- Implement BootFlowService with IStatesController injection and RunFlowAsync logic
- Add Splash → Load → Menu loop with cancellation support in boot flow
- Create IMenuRestartSignal interface for menu restart coordination
- Implement MenuRestartSignal using UniTaskCompletionSource
- Update MenuState to wait for restart signal instead of completing immediately
- Register MenuRestartSignal as singleton in GameLifetimeScope DI container

Выполнена задача TASK-0003 и реализован поток загрузки:
- Реализован BootFlowService с внедрением IStatesController и логикой RunFlowAsync
- Добавлен цикл Splash → Load → Menu с поддержкой отмены в потоке загрузки
- Создан интерфейс IMenuRestartSignal для координации перезапуска меню
- Реализован MenuRestartSignal с использованием UniTaskCompletionSource
- Обновлён MenuState для ожидания сигнала перезапуска вместо немедленного завершения
- Зарегистрирован MenuRestartSignal как синглтон в DI контейнере GameLifetimeScope

Assets/Scripts/Boot/Flow/BootFlowService.cs

@@ -1,19 +1,42 @@
 using System.Threading;
 using Cysharp.Threading.Tasks;
+using QuizPleaseTest.Boot.States;
 using QuizPleaseTest.Common.Services;
+using QuizPleaseTest.Common.StateMachine;
 
 namespace QuizPleaseTest.Boot.Flow
 {
     public class BootFlowService : Service, IBootFlowService
     {
-        public override UniTask InitializeAsync(CancellationToken ct)
+        private readonly IStatesController<BootStateCode> _statesController;
+
+        public BootFlowService(IStatesController<BootStateCode> statesController)
         {
-            return UniTask.CompletedTask;
+            _statesController = statesController;
+        }
+
+        public override async UniTask InitializeAsync(CancellationToken ct)
+        {
+            await RunFlowAsync(ct);
         }
 
         public override UniTask ReleaseAsync(CancellationToken ct)
         {
             return UniTask.CompletedTask;
         }
+
+        private async UniTask RunFlowAsync(CancellationToken ct)
+        {
+            await _statesController.EnterStateAsync(BootStateCode.Splash, ct);
+            await _statesController.EnterStateAsync(BootStateCode.Load, ct);
+
+            while (!ct.IsCancellationRequested)
+            {
+                await _statesController.EnterStateAsync(BootStateCode.Menu, ct);
+                await _statesController.EnterStateAsync(BootStateCode.Load, ct);
+            }
+
+            ct.ThrowIfCancellationRequested();
+        }
     }
 }

Assets/Scripts/Boot/Flow/IMenuRestartSignal.cs

@@ -0,0 +1,11 @@
+using System.Threading;
+using Cysharp.Threading.Tasks;
+
+namespace QuizPleaseTest.Boot.Flow
+{
+    public interface IMenuRestartSignal
+    {
+        UniTask WaitAsync(CancellationToken ct);
+        void RequestRestart();
+    }
+}

Assets/Scripts/Boot/Flow/IMenuRestartSignal.cs.meta

@@ -0,0 +1,11 @@
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+MonoImporter:
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+  serializedVersion: 2
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Assets/Scripts/Boot/Flow/MenuRestartSignal.cs

@@ -0,0 +1,23 @@
+using System.Threading;
+using Cysharp.Threading.Tasks;
+
+namespace QuizPleaseTest.Boot.Flow
+{
+    public class MenuRestartSignal : IMenuRestartSignal
+    {
+        private UniTaskCompletionSource _restartCompletionSource;
+
+        public UniTask WaitAsync(CancellationToken ct)
+        {
+            ct.ThrowIfCancellationRequested();
+
+            _restartCompletionSource = new UniTaskCompletionSource();
+            return _restartCompletionSource.Task.AttachExternalCancellation(ct);
+        }
+
+        public void RequestRestart()
+        {
+            _restartCompletionSource?.TrySetResult();
+        }
+    }
+}

Assets/Scripts/Boot/Flow/MenuRestartSignal.cs.meta

@@ -0,0 +1,11 @@
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