types(Skeleton): add SkeletonAvatarShape type (#9605)

packages/vant/src/skeleton/README.md

@@ -73,6 +73,14 @@ export default {
 | avatar-size | Size of avatar placeholder | _number \| string_ | `32px` |
 | avatar-shape | Shape of avatar placeholder，can be set to `square` | _string_ | `round` |
 
+### Types
+
+The component exports the following type definitions:
+
+```ts
+import type { SkeletonAvatarShape } from 'vant';
+```
+
 ## Theming
 
 ### CSS Variables

packages/vant/src/skeleton/README.zh-CN.md

@@ -79,6 +79,14 @@ export default {
 | avatar-size | 头像占位图大小 | _number \| string_ | `32px` |
 | avatar-shape | 头像占位图形状，可选值为 `square` | _string_ | `round` |
 
+### 类型定义
+
+组件导出以下类型定义：
+
+```ts
+import type { SkeletonAvatarShape } from 'vant';
+```
+
 ## 主题定制
 
 ### 样式变量

packages/vant/src/skeleton/index.ts

@@ -1,5 +1,6 @@
 import { withInstall } from '../utils';
-import _Skeleton from './Skeleton';
+import _Skeleton, { SkeletonAvatarShape } from './Skeleton';
 
 export const Skeleton = withInstall(_Skeleton);
 export default Skeleton;
+export type { SkeletonAvatarShape };