[Feature] 新增链接失效自动分组功能

当友链无法访问或检测失败时, 自动移动到指定分组

新增设置项:
- 是否启用自动分组
- 是否启用自动检测

> 插件已有手动检测功能, 新增一个自动检测

- 自动检测频率
- 指定目标分组

Start by reading the plugin's existing manual link-detection entry point and the current settings and group-management behavior. Trace how failed or inaccessible links are represented and moved between groups. Done means the four settings work, automatic detection runs at the configured frequency, and failed links are moved to the selected group without breaking manual detection.

Written by the indexing model from the issue text.