github.com/cloudwego/eino-ext/adk/backend/local.Local 不支持软链接目录

**Describe the bug**

`github.com/cloudwego/eino-ext/adk/backend/local.Local` 不支持软链接。
当目录是软链接的时候，直接无视了。
是故意这样设计还是真的有问题？

**To Reproduce**

比如 skills 目录，是软链接的时候，会被无视。

**Expected behavior**

跟随软链接。

**Version:**

0.2.3

**Environment:**

GOVERSION='go1.26.1'

Start at github.com/cloudwego/eino-ext/adk/backend/local.Local and reproduce the behavior with a skills directory that is a symbolic link. Trace how directory entries are handled and confirm that linked directories are currently skipped. Done means Local follows the link and includes the linked directory as expected.

Written by the indexing model from the issue text.