dsh-video-length: Video Length Recommendation

The DeepSeek Harness (DSH) plugin `uckkk/dsh-video-length` is specifically designed to address the need for precise video duration calculation in model inference. Implemented entirely in Node.js with no network dependencies, it can calculate video duration in detail based on input parameters. Once installed, its tool can be invoked within a session. Before use, please review the source code and license, and ensure that the dependencies `@deepseek-ai/cordis` and `@deepseek-ai/dsh-tools` are installed.