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/enemies/EnemyBase.ts

@@ -2,6 +2,7 @@ import type Phaser from 'phaser'
 import { GameManager } from '../GameManager'
 import { HUD_HEIGHT } from '../constants'
 import { getCellSize } from '../mapRenderer'
+import { AudioEngine } from '../AudioEngine'
 import { ALL_MAPS } from '../data/mapConfigs'
 
 export interface PathPoint { x: number; y: number }
@@ -228,6 +229,8 @@ export abstract class EnemyBase {
     this.isDead = true
     const reward = this.hcRewardBonus ? this.hcReward * 2 : this.hcReward
     GameManager.getInstance().addHC(reward)
+    // 怪物死亡音效（碎纸机）
+    AudioEngine.getInstance().playEnemyDeath()
     this.onDeath()
     this.destroy()
   }