feat(task-0006): implement menu restart button and signal coordination

- Update MenuUIViewModel with IMenuRestartSignal dependency and Restart() method
- Add RestartButton to MenuUIView with listener management in Initialize/Release
- Connect MenuUIView click handler to ViewModel.Restart() callback
- Fix race condition in MenuRestartSignal.RequestRestart() by nulling completion source first
- Wrap MenuState.WaitAsync() in try-catch for proper view cleanup on cancellation
- Update TASK-0006 status to Ready

Выполнена задача TASK-0006: реализована кнопка Restart и координация сигналов

- Обновлён MenuUIViewModel с зависимостью IMenuRestartSignal и методом Restart()
- Добавлена кнопка RestartButton в MenuUIView с управлением слушателями в Initialize/Release
- Подключен обработчик кликов MenuUIView к колбэку ViewModel.Restart()
- Исправлено состояние гонки в MenuRestartSignal.RequestRestart() путем обнуления completion source
- Обёрнут WaitAsync в MenuState в try-catch для корректной очистки view при отмене
- Обновлён статус TASK-0006 до Ready

Assets/Scenes/SampleScene.unity

@@ -381,6 +381,7 @@ GameObject:
   m_Component:
   - component: {fileID: 1000000302}
   - component: {fileID: 1000000303}
+  - component: {fileID: 1000000304}
   m_Layer: 0
   m_Name: MenuView
   m_TagString: Untagged
@@ -414,3 +415,48 @@ MonoBehaviour:
   m_Script: {fileID: 11500000, guid: b3333333333333333333333333333333, type: 3}
   m_Name: 
   m_EditorClassIdentifier: 
+  <RestartButton>k__BackingField: {fileID: 1000000304}
+--- !u!114 &1000000304
+MonoBehaviour:
+  m_ObjectHideFlags: 0
+  m_CorrespondingSourceObject: {fileID: 0}
+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
+  m_GameObject: {fileID: 1000000301}
+  m_Enabled: 1
+  m_EditorHideFlags: 0
+  m_Script: {fileID: 11500000, guid: 4e29b1a8efbd4b44bb3f3716e73f07ff, type: 3}
+  m_Name: 
+  m_EditorClassIdentifier: 
+  m_Navigation:
+    m_Mode: 3
+    m_WrapAround: 0
+    m_SelectOnUp: {fileID: 0}
+    m_SelectOnDown: {fileID: 0}
+    m_SelectOnLeft: {fileID: 0}
+    m_SelectOnRight: {fileID: 0}
+  m_Transition: 1
+  m_Colors:
+    m_NormalColor: {r: 1, g: 1, b: 1, a: 1}
+    m_HighlightedColor: {r: 0.88235295, g: 0.88235295, b: 0.88235295, a: 1}
+    m_PressedColor: {r: 0.69803923, g: 0.69803923, b: 0.69803923, a: 1}
+    m_SelectedColor: {r: 0.88235295, g: 0.88235295, b: 0.88235295, a: 1}
+    m_DisabledColor: {r: 0.52156866, g: 0.52156866, b: 0.52156866, a: 0.5019608}
+    m_ColorMultiplier: 1
+    m_FadeDuration: 0.1
+  m_SpriteState:
+    m_HighlightedSprite: {fileID: 0}
+    m_PressedSprite: {fileID: 0}
+    m_SelectedSprite: {fileID: 0}
+    m_DisabledSprite: {fileID: 0}
+  m_AnimationTriggers:
+    m_NormalTrigger: Normal
+    m_HighlightedTrigger: Highlighted
+    m_PressedTrigger: Pressed
+    m_SelectedTrigger: Selected
+    m_DisabledTrigger: Disabled
+  m_Interactable: 1
+  m_TargetGraphic: {fileID: 0}
+  m_OnClick:
+    m_PersistentCalls:
+      m_Calls: []