refactor: 调整卡牌等级逻辑，新增基础池等级字段

1. 新增base_pool_lv字段存储英雄初始池等级
2. 替换多处直接使用pool_lv的逻辑，优先使用base_pool_lv
3. 移除预制体中废弃的pool_lv_node节点

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

@@ -53,6 +53,7 @@ export interface CardConfig {
     pool_lv: CardLV
     hero_lv?: number
     card_lv?:number
+    base_pool_lv?: number
     
     // 技能卡扩展属性
     name?: string           // 卡牌名称
@@ -116,7 +117,8 @@ HeroList.forEach(uuid => {
             weight: baseWeight,
             pool_lv: pLv as CardLV,
             kind: CKind.Hero,
-            hero_lv: targetHeroLv
+            hero_lv: targetHeroLv,
+            base_pool_lv: basePoolLv
         });
     }
 });