dsh-envsel: Selecting Python, R, and CLI Environments in DSH Sessions

DSH-EnVSel is a standalone plugin for DeepSeek Harness (DSH), maintained by beihzb, designed to address the need for binding different language environments to different sessions within the same DSH instance. The plugin provides independent environment slots for Python, R, and CLI tools, supporting selection from conda, standalone R installations, WSL distributions, or user-defined paths, with selections persisted to a local JSON file that remains effective after restarts. Users can read, assign, pin, or clear environment settings via the `/env` command in chat or the `session_env` model tool. The plugin exposes `DSH_ENV_PYTHON`, `DSH_ENV_RSCRIPT`, and `D` within shell invocations.