ADK/TaskList: read task file x.json failed, err: file not found: /x.json

**Describe the bug**

Adk PlanTask中间件BUG，ReadTask报错：`TaskList read task file 1.json failed, err: file not found: /1.json`

func listTasks(ctx context.Context, backend Backend, baseDir string) 中，backend.LsInfo返回的只是文件名而非完整文件路径，但是后续backend.Read的时候没有拼接baseDir。

**Version:**

v8.0.6

Locate the listTasks entry point in the ADK/TaskList middleware and inspect how backend.LsInfo results are passed to backend.Read. Ensure the baseDir is included when resolving each task file, then verify that task files are read from the configured directory rather than the filesystem root.

Written by the indexing model from the issue text.