fix(config): 调整英雄卡抽取权重随等级递减逻辑

将原本固定的英雄抽取权重改为按等级几何递减，高等级英雄更难抽取，优化卡池抽取概率梯度

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

@@ -102,17 +102,26 @@ function getHeroCost(cardLv: number): number {
     return 15;
 }
 
+/**
+ * 英雄卡按 card_lv 分配抽取权重（几何递减，高等级越稀有）。
+ * 梯度：lv1=40, lv2=25, lv3=15, lv4=8, lv5=3
+ */
+const HERO_WEIGHT_BY_LV: Record<number, number> = {
+    1: 40, 2: 25, 3: 15, 4: 8, 5: 3,
+};
+function getHeroWeight(cardLv: number): number {
+    return HERO_WEIGHT_BY_LV[cardLv] ?? HERO_WEIGHT_BY_LV[1];
+}
+
 HeroList.forEach(uuid => {
     const hero = HeroInfo[uuid];
     if (!hero) return;
 
-    const baseWeight = 25;
-
     CardPoolList.push({
         uuid: hero.uuid,
         type: CardType.Hero,
         cost: getHeroCost(hero.card_lv ?? 1),
-        weight: baseWeight,
+        weight: getHeroWeight(hero.card_lv ?? 1),
         card_lv: hero.card_lv ?? 1,
         kind: CKind.Hero,
         hero_lv: 1,