refactor(battle): 重构战斗目标查找与位置管理逻辑

新增全局位置网格系统，用于按索引存储敌我单位实体ID：
-  在SingletonModuleComp添加heroGrid与monGrid数组
-  为HeroAttrsComp新增posIndex字段记录位置索引并初始化

优化战斗核心流程：
-  重构MissionHeroComp的位置选择逻辑，拆分方法返回位置索引而非直接坐标，优化位置占用检测
-  重构SCastSystem的目标查找与收集逻辑，改用网格遍历替代全量实体查询，大幅提升性能
-  统一三路单位的查找优先级，简化代码提升可维护性
-  完善Hero与Monster的创建销毁流程，同步更新网格的单位注册与注销信息

assets/script/game/map/MissionHeroComp.ts

@@ -132,11 +132,14 @@ export class MissionHeroComp extends CCComp {
             if (model && view) {
                 if (model.is_dead) {
                     view.alive();
-                    const landingPos = this.pickPositionForHero([hero.eid]);
+                    const posIndex = this.pickPositionIndexForHero([hero.eid]);
+                    const landingPos = MissionHeroComp.HERO_POSITIONS[posIndex];
                     // 不再直接设置位置，而是播放下落入场动画
                     // 计算出出生点（空中）
                     const spawnPos: Vec3 = v3(landingPos.x, landingPos.y + MissionHeroComp.HERO_DROP_HEIGHT, 0);
                     view.node.setPosition(spawnPos);
+                    model.posIndex = posIndex;
+                    if (posIndex >= 0) smc.mission.heroGrid[posIndex] = hero.eid;
                     hero.playDropAnim(spawnPos, landingPos.y);
                 }
                 model.dirty_hp = true;
@@ -171,7 +174,7 @@ export class MissionHeroComp extends CCComp {
      * 动态分配英雄上场的位置
      * @param excludeEids 排除计算的实体ID数组（避免复活或合成时把自己算成占据的位置）
      */
-    private pickPositionForHero(excludeEids: number[] = []): Vec3 {
+    private pickPositionIndexForHero(excludeEids: number[] = []): number {
         const heroes = this.getAllHeroes().filter(h => {
             const m = h.get(HeroAttrsComp);
             return m && !m.is_dead && !excludeEids.includes(h.eid);
@@ -179,28 +182,20 @@ export class MissionHeroComp extends CCComp {
 
         const occupied = new Set<number>();
         for (const h of heroes) {
-            const move = h.get(MoveComp); // MoveComp 记录了英雄当前的目标位置
-            if (move) {
-                for (let i = 0; i < MissionHeroComp.HERO_POSITIONS.length; i++) {
-                    const pos = MissionHeroComp.HERO_POSITIONS[i];
-                    if (Math.abs(move.targetX - pos.x) < 2 && Math.abs(move.baseY - pos.y) < 2) {
-                        occupied.add(i);
-                        break;
-                    }
-                }
-            }
+            const m = h.get(HeroAttrsComp);
+            if (m && m.posIndex >= 0) occupied.add(m.posIndex);
         }
         
         // 优先中前(1) -> 上前(0) -> 下前(2) -> 中后(4) -> 上后(3) -> 下后(5)
         const slotPriority = [1, 0, 2, 4, 3, 5];
         for (const idx of slotPriority) {
             if (!occupied.has(idx)) {
-                return MissionHeroComp.HERO_POSITIONS[idx];
+                return idx;
             }
         }
         
         // 溢出：默认中前
-        return MissionHeroComp.HERO_POSITIONS[1];
+        return 1;
     }
 
     /**
@@ -217,9 +212,10 @@ export class MissionHeroComp extends CCComp {
         console.log("addHero uuid:",uuid)
         let hero = ecs.getEntity<Hero>(Hero);
         let scale = 1
-        const landingPos = this.pickPositionForHero();
+        const posIndex = this.pickPositionIndexForHero();
+        const landingPos = MissionHeroComp.HERO_POSITIONS[posIndex];
         let spawnPos:Vec3 = v3(landingPos.x, landingPos.y + MissionHeroComp.HERO_DROP_HEIGHT, 0);
-        hero.load(spawnPos,scale,uuid,landingPos.y,hero_lv,pool_lv);
+        hero.load(spawnPos,scale,uuid,landingPos.y,hero_lv,pool_lv,posIndex);
         
         // 召唤完成后，派发事件以更新英雄面板
         const model = hero.get(HeroAttrsComp);
@@ -246,14 +242,19 @@ export class MissionHeroComp extends CCComp {
      * @param targetPos 指定生成位置
      * @returns        实际生成的英雄等级
      */
-    private addMergedHero(uuid:number, hero_lv:number, pool_lv:number, ap:number, hp_max:number, targetPos?: Vec3): number {
+    private addMergedHero(uuid:number, hero_lv:number, pool_lv:number, ap:number, hp_max:number, targetPosIndex?: number, targetPos?: Vec3): number {
         console.log("addMergedHero uuid:",uuid)
         let hero = ecs.getEntity<Hero>(Hero);
         let scale = 1
         
-        const landingPos = targetPos || this.pickPositionForHero();
+        let posIndex = targetPosIndex;
+        let landingPos = targetPos;
+        if (posIndex === undefined || posIndex < 0 || !landingPos) {
+            posIndex = this.pickPositionIndexForHero();
+            landingPos = MissionHeroComp.HERO_POSITIONS[posIndex];
+        }
         let spawnPos:Vec3 = v3(landingPos.x, landingPos.y + MissionHeroComp.HERO_DROP_HEIGHT, 0);
-        hero.load(spawnPos,scale,uuid,landingPos.y,hero_lv,pool_lv);
+        hero.load(spawnPos,scale,uuid,landingPos.y,hero_lv,pool_lv,posIndex);
         
         // 召唤完成后，派发事件以更新英雄面板
         const model = hero.get(HeroAttrsComp);
@@ -481,14 +482,14 @@ export class MissionHeroComp extends CCComp {
             sumHpMax += model.hp_max;
         }
         
-        // 计算目标出生点（提前排除素材英雄所占的位置）
-        const landingPos = this.pickPositionForHero(mergeEids);
+        const posIndex = this.pickPositionIndexForHero(mergeEids);
+        const landingPos = MissionHeroComp.HERO_POSITIONS[posIndex];
         const spawnPos:Vec3 = v3(landingPos.x, landingPos.y + MissionHeroComp.HERO_DROP_HEIGHT, 0);
         
         // 汇聚 → 特效 → 生成
         await this.mergeDestroyAtBirth(mergeHeroes, spawnPos);
         await this.playMergeBoomFx(spawnPos);
-        return this.addMergedHero(uuid, Math.min(this.merge_max_lv, hero_lv + 1), pool_lv, sumAp, sumHpMax, landingPos);
+        return this.addMergedHero(uuid, Math.min(this.merge_max_lv, hero_lv + 1), pool_lv, sumAp, sumHpMax, posIndex, landingPos);
     }
 
     /**