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/map/HInfoComp.ts

@@ -275,7 +275,7 @@ export class HInfoComp extends CCComp {
             this.BG_node.children.forEach(child => {
                 child.active = (child.name === kindName);
                 const bg = child.getComponent(CardBgComp);
-                if (bg) child.active ? bg.apply(this.model.pool_lv ?? 1) : bg.clear();
+                if (bg) child.active ? bg.apply(this.model.base_pool_lv ?? this.model.pool_lv ?? 1) : bg.clear();
             });
         }