dsh-websearch-custom: Configurable OpenAI Responses Web-Search Tool Provider for DeepSeek Harness

dsh-websearch-custom is an open-source plugin for DeepSeek Harness that lets users take over the built-in web search feature by configuring an OpenAI Responses-compatible endpoint. It registers a provider named `custom-openai`, includes no default configuration, and leaves all key parameters (such as endpoint, model, and API key) to the user. It supports dynamic configuration via the browser settings interface or a configuration file, uses native search tools instead of web scraping, and strictly relies on URL citations returned by the endpoint. To install it, use the plugin command and set the `searchProvider` for the `web` channel to it.