dsh-plugin-tavily: Tavily Web Search Plugin for DeepSeek Harness

dsh-plugin-tavily is a web search plugin designed for DeepSeek Harness (DSH), aiming to replace the default search engine via the Tavily service to address issues such as fragmented configuration and inconvenient verification. This plugin registers a `tavily` provider with the `ctx.web` seam, supporting dual configuration modes through the WebUI settings card and `cordis.patch.yml`, with the latter having the highest priority. Core features include comprehensive Tavily search parameter customization, multiple preset scenarios, connectivity testing, and usage monitoring. For data extraction, it offers optional providers based on Tavily Extract and Firecrawl. Engineering capabilities cover persistent caching, 429 retry mechanisms, and rate limiting.