feat: add BossPhaseChange game event

assets/script/game/common/config/GameEvent.ts

@@ -116,5 +116,7 @@ export enum GameEvent {
     NextSection = "NextSection",
     /** 结算弹窗点击"再来一次"（payload 为空，MissionComp 据此重开本关） */
     RestartMission = "RestartMission",
+    /** Boss 阶段切换（payload: { eid, planId, fromPhase, toPhase }，表现层监听此事件实现演出；eid 定位实体，勿持裸引用） */
+    BossPhaseChange = "BossPhaseChange",
 }