dsh-s1: Register s1 search capability as a native DSH tool

dsh-s1 is a DeepSeek Harness (DSH) plugin maintained by superagents-lab, licensed under the MIT license and requiring Node.js >= 20.0.0. This plugin registers s1 search capabilities as a first-class tool, allowing the model to directly invoke `s1_search`, `s1_news`, `s1_crawl`, `s1_sitemap`, and `s1_trending` without executing additional shell commands, while also providing bundled skills to assist with model selection, tools, and parameters. Currently, the functions `s1_screenshot` and `s1_deepcrawl` are not yet implemented, nor is the OAuth flow. When installing, it can be accessed via `dsh plugi...`