Use dsh-video-downloader to detect and download web videos in DeepSeek Harness

### 正式翻译（符合技术文档规范）： dsh-video-downloader is a DSH tool plugin maintained by zimai233. It packages media recognition into three agent tools: 1. `video_analyze`: Judges the site and whether the input URL points to a media resource 2. `video_download`: Streams and writes direct links to the `./downloads/` directory 3. `video_quality_parse`: Extracts definition and extension information using regular expressions It is licensed under MIT. Install it via `dsh plugin add github:zimai233/dsh-video-downloader`. This plugin does not crawl playback pages or bypass DRM, has a 60-second download timeout, and is only applicable to content that the user has legitimate access rights to.