dsh-plugin-terminal: Adding a Bottom Terminal Panel to the DSH Web GUI

dsh-plugin-terminal is a bottom terminal panel plugin developed specifically for the DeepSeek Harness (DSH) Web GUI, designed to allow users to use multi-tab Shell at the bottom of the page without leaving the browser. Based on node-pty, the plugin supports ConPTY on Windows and openpty on Linux/macOS, addressing the needs of executing commands in parallel within the chat interface, viewing logs, and running full-screen terminal programs like Codex and Claude Code. Core features include: supporting the creation, closure, and restart of multi-tab sessions, with processes continuing to run when switching tabs; persistent storage of session status, working directories, and scrollback history, which can be restored after page refresh or restart; compatibility with xterm.js 6 features, and support for t