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/Animation/OpeningFlowController.cs

@@ -127,7 +127,7 @@ public class OpeningFlowController : MonoBehaviour
 
         // Step 2: Shoot + 篮球音效
         Debug.Log("[OpeningFlow] Step2: Shoot 开始");
-        if (_basketballClip != null) AudioSource.PlayClipAtPoint(_basketballClip, transform.position);
+        if (AudioManager.I != null) AudioManager.I.PlayBasketballSfx();
         if (_manAnimator != null) { _manAnimator.Play("Shoot", 0, 0f); Debug.Log("[OpeningFlow] Shoot Play 已触发"); }
         yield return new WaitForSeconds(3.15f);
         Debug.Log("[OpeningFlow] Step2: Shoot 结束");
@@ -136,7 +136,7 @@ public class OpeningFlowController : MonoBehaviour
         Debug.Log("[OpeningFlow] Step3: manfull 开始");
         if (_manAnimator != null) { _manAnimator.Play("manfull", 0, 0f); }
         yield return new WaitForSeconds(2.1f);
-        if (_manCallClip != null) AudioSource.PlayClipAtPoint(_manCallClip, transform.position);
+        if (AudioManager.I != null) AudioManager.I.PlayManCallSfx();
         Debug.Log("[OpeningFlow] manfull 播放完成, 停留 2s");
         yield return new WaitForSeconds(2f);