fix: 修复FixationPanel和ExperimentPanel的按钮无响应与缩放问题

- FixationPanel/ExperimentPanel: raycastTarget设为false，防止背景Image阻断子按钮点击
- FixationPanel/ExperimentPanel: RectTransform anchor改为(0,0)-(1,1)全屏拉伸，与HomePagePanel/ModeSelectPanel一致
- 删除旧版Canvas/BtnFixationBack遗留按钮
- Panel背景Image不再作为raycast目标，保证子按钮可点击

Assets/Scenes/main.unity

@@ -733,10 +733,10 @@ RectTransform:
   - {fileID: 617526393}
   m_Father: {fileID: 1642393469}
   m_LocalEulerAnglesHint: {x: 0, y: 0, z: 0}
-  m_AnchorMin: {x: 0.5, y: 0.5}
-  m_AnchorMax: {x: 0.5, y: 0.5}
-  m_AnchoredPosition: {x: 0.00016403, y: 0.0000095367}
-  m_SizeDelta: {x: 2094.7, y: 1080}
+  m_AnchorMin: {x: 0, y: 0}
+  m_AnchorMax: {x: 1, y: 1}
+  m_AnchoredPosition: {x: 0, y: 0}
+  m_SizeDelta: {x: 0, y: 0}
   m_Pivot: {x: 0.5, y: 0.5}
 --- !u!114 &200058302
 MonoBehaviour:
@@ -752,7 +752,7 @@ MonoBehaviour:
   m_EditorClassIdentifier: 
   m_Material: {fileID: 0}
   m_Color: {r: 1, g: 1, b: 1, a: 0}
-  m_RaycastTarget: 1
+  m_RaycastTarget: 0
   m_RaycastPadding: {x: 0, y: 0, z: 0, w: 0}
   m_Maskable: 1
   m_OnCullStateChanged:
@@ -5672,7 +5672,7 @@ MonoBehaviour:
   m_PrefabInstance: {fileID: 0}
   m_PrefabAsset: {fileID: 0}
   m_GameObject: {fileID: 1642393464}
-  m_Enabled: 1
+  m_Enabled: 0
   m_EditorHideFlags: 0
   m_Script: {fileID: 11500000, guid: 11edd93e0776546a3b8545535d7dd5e1, type: 3}
   m_Name: 
@@ -5719,6 +5719,8 @@ MonoBehaviour:
   _homePagePanel: {fileID: 1037678401}
   _modeSelectPanel: {fileID: 1819847500}
   _fixationPanel: {fileID: 1813870029}
+  _experimentPanel: {fileID: 0}
+  _btnExperimentBack: {fileID: 0}
   _uiManager: {fileID: 1642393470}
   _btnStart: {fileID: 1701102418}
   _btnExit: {fileID: 1171419708}
@@ -6483,7 +6485,7 @@ GameObject:
   m_Icon: {fileID: 0}
   m_NavMeshLayer: 0
   m_StaticEditorFlags: 0
-  m_IsActive: 0
+  m_IsActive: 1
 --- !u!224 &1813870030
 RectTransform:
   m_ObjectHideFlags: 0
@@ -6501,10 +6503,10 @@ RectTransform:
   - {fileID: 1329058528}
   m_Father: {fileID: 1642393469}
   m_LocalEulerAnglesHint: {x: 0, y: 0, z: 0}
-  m_AnchorMin: {x: 0.5, y: 0.5}
-  m_AnchorMax: {x: 0.5, y: 0.5}
-  m_AnchoredPosition: {x: 0.00016403, y: 0.0000095367}
-  m_SizeDelta: {x: 2094.7, y: 1080}
+  m_AnchorMin: {x: 0, y: 0}
+  m_AnchorMax: {x: 1, y: 1}
+  m_AnchoredPosition: {x: 0, y: 0}
+  m_SizeDelta: {x: 0, y: 0}
   m_Pivot: {x: 0.5, y: 0.5}
 --- !u!114 &1813870031
 MonoBehaviour:
@@ -6520,7 +6522,7 @@ MonoBehaviour:
   m_EditorClassIdentifier: 
   m_Material: {fileID: 0}
   m_Color: {r: 1, g: 1, b: 1, a: 0.95}
-  m_RaycastTarget: 1
+  m_RaycastTarget: 0
   m_RaycastPadding: {x: 0, y: 0, z: 0, w: 0}
   m_Maskable: 1
   m_OnCullStateChanged: