feat: 调整游戏难度并优化UI布局

- 降低卡池等级上限和英雄等级上限以简化前期难度
- 重新平衡前四波怪物配置，使难度曲线更平缓
- 移除卡池升级功能并隐藏相关UI按钮
- 调整角色控制器UI元素的位置和尺寸
- 修改加载界面元素的缩放比例

assets/resources/loading/prefab/loading.prefab

@@ -1819,8 +1819,8 @@
     },
     "_lscale": {
       "__type__": "cc.Vec3",
-      "x": 1.5,
-      "y": 1.5,
+      "x": 2,
+      "y": 2,
       "z": 1
     },
     "_mobility": 0,
@@ -1847,8 +1847,8 @@
     },
     "_contentSize": {
       "__type__": "cc.Size",
-      "width": 421,
-      "height": 132
+      "width": 218,
+      "height": 166
     },
     "_anchorPoint": {
       "__type__": "cc.Vec2",
@@ -1884,12 +1884,12 @@
       "a": 255
     },
     "_spriteFrame": {
-      "__uuid__": "cb93c900-b440-4571-91d1-7da1636e3d73@a557f",
+      "__uuid__": "cb93c900-b440-4571-91d1-7da1636e3d73@e5c7b",
       "__expectedType__": "cc.SpriteFrame"
     },
     "_type": 0,
     "_fillType": 0,
-    "_sizeMode": 0,
+    "_sizeMode": 1,
     "_fillCenter": {
       "__type__": "cc.Vec2",
       "x": 0,