feat: 音频系统统一重写—AudioManager管理全部音频

新增 AudioManager.cs 挂在 [Managers] 上:
- _bgSource: 背景音乐(首页/实验), spatialBlend=0, BgVolume可调
- _sfxSource: 音效(篮球/manCall), Stop()可打断
- _voiceSource: 语音中断播放

替换:
- PageController: BGMController→AudioManager.I
- OpeningFlowController: PlayClipAtPoint→AudioManager.I.PlayBasketball/ManCallSfx
- 删除 BGMController.cs
- 删除旧 AudioManager.cs(Assets/Scripts/Audio/旧版)

Assets/Scripts/UI/PageController.cs

@@ -121,8 +121,8 @@ public class PageController : MonoBehaviour
 
         if (_uiManager != null)
             _uiManager.enabled = (page == Page.Experiment);
-        if (page == Page.Home) BGMController.PlayHomeBg();        // 背景音乐: 首页播 homeBg, 选固定方式时停, 实验启动时播 experimentBg
-        if (page == Page.Home) BGMController.PlayHomeBg();
+        if (page == Page.Home) AudioManager.I.PlayHomeBg();        // 背景音乐: 首页播 homeBg, 选固定方式时停, 实验启动时播 experimentBg
+        if (page == Page.Home) AudioManager.I.PlayHomeBg();
         Debug.Log($"PageController（编辑器预览）: 切换到 [{page}]");
     }
 #endif
@@ -224,7 +224,7 @@ public class PageController : MonoBehaviour
         Debug.Log($"PageController: GameManager 已设置 Mode=[{gm.CurrentMode}] Fixation=[{gm.CurrentFixationMethod}]");
 
         // 隐藏所有UI面板，准备播放片头动画
-        BGMController.StopBgMusic();
+        AudioManager.I.StopBgMusic();
         HideAllPages();
 
         // 找到 OpeningFlowController 播放片头动画
@@ -267,7 +267,7 @@ public class PageController : MonoBehaviour
     {
         Debug.Log("PageController: [ActivateExperimentObjects] 显示实验物件");
 
-        BGMController.PlayExperimentBg();
+        AudioManager.I.PlayExperimentBg();
 
         var allObjects = FindObjectsOfType<GameObject>(true);
         foreach (var go in allObjects)