feat(game): 添加全套音效系统（背景BGM+7种攻击音+波次/Boss/死亡/建塔音效），纯Web Audio API合成

game/towers/OutsourceTower.ts

@@ -1,5 +1,6 @@
 import type Phaser from 'phaser'
 import { TowerBase } from './TowerBase'
+import { AudioEngine } from '../AudioEngine'
 import type { EnemyBase } from '../enemies/EnemyBase'
 
 /**
@@ -15,6 +16,7 @@ export class OutsourceTower extends TowerBase {
   }
 
   attack(target: EnemyBase): void {
+    AudioEngine.getInstance().playOutsourceAttack()
     // 5% 概率 Bug 反弹（精力归零）
     if (Math.random() < 0.05) {
       this.stamina = 0