refactor(ui): 重构卡片背景预制体与样式

1. 新增boxsbg通用卡片背景预制体
2. 调整ui5.plist的边框内边距配置
3. 重构sbox.prefab，替换为统一的卡片背景组件

assets/resources/gui/auie/boxsbg.prefab.meta

@@ -0,0 +1,13 @@
+{
+  "ver": "1.1.50",
+  "importer": "prefab",
+  "imported": true,
+  "uuid": "735b5b91-006f-42eb-b097-dc69fa0884ca",
+  "files": [
+    ".json"
+  ],
+  "subMetas": {},
+  "userData": {
+    "syncNodeName": "boxsbg"
+  }
+}