fix: bg音乐缓入+语音打断+代码碎片清理

- PlayHomeBg/PlayExperimentBg 增加 FadeInBg 缓入协程(1.5s)
- TouchPositionHandler 使用静态共享 AudioSource 避免语音重叠
- 清理 PageController 中因多次编辑产生的代码碎片和括号混乱

Assets/Scripts/Interaction/TouchPositionHandler.cs

@@ -49,7 +49,7 @@ public class TouchPositionHandler : MonoBehaviour
 
         if (voiceClip != null)
         {
-            AudioSource.PlayClipAtPoint(voiceClip, transform.position);
+            PlaySharedVoice();
             Debug.Log($"[TouchPosition] 播放语音: {voiceClip.name}");
         }
 
@@ -67,4 +67,20 @@ public class TouchPositionHandler : MonoBehaviour
             Debug.Log($"[TouchPosition] {name} → {nextTouchObject.name} 显示");
         }
     }
+
+    private static AudioSource _sharedVoice;
+
+    private void PlaySharedVoice()
+    {
+        if (voiceClip == null) return;
+        if (_sharedVoice == null)
+        {
+            var go = GameObject.Find("[Managers]");
+            if (go != null) _sharedVoice = go.AddComponent<AudioSource>();
+            else { var g = new GameObject("SharedVoice"); _sharedVoice = g.AddComponent<AudioSource>(); }
+        }
+        _sharedVoice.Stop();
+        _sharedVoice.clip = voiceClip;
+        _sharedVoice.Play();
+    }
 }