dsh-auth-gate: DeepSeek Harness Authentication and Security Hardening Plugin

`dsh-auth-gate` is a security hardening plugin for DeepSeek Harness, designed to address the risk of unauthorized access to local development tools in network scenarios such as Docker and reverse proxies. It provides Bearer token authentication for HTTP and WebSocket routes and supports session login and fail-closed mode. The plugin manages credentials through environment variables and requires specifying a Patch file after installation to enable it. Note that it does not support ACP/SDK channels, does not record audit logs, and lacks user isolation; in reverse proxy scenarios, it is recommended to configure rate limiting at the edge layer.