dsh-context-proxy: On-demand Context Retrieval for DeepSeek Harness

dsh-context-proxy is a lightweight context retrieval plugin for DeepSeek Harness (DSH), designed to address the need for models to read persisted session history on demand, thereby avoiding the loading of the full context. The plugin provides three core tools: context_query for finding matches by field, context_slice for reading a single event along with its limited surrounding window, and context_grep for text retrieval, supporting the return of locatable references (e.g., session:<seq> or path:line). Users can install and enable the plugin via the `dsh plugin` command from GitHub or a local path. Its dependency mechanism clearly distinguishes between optional and hard dependencies, quickly returning an error instead of blocking if the backend service is missing. contex