dsh-permission-gate: DSH Process-Level Access Gate and Tool Brake

`dsh-permission-gate` is a security plugin for DeepSeek Harness designed to address access risks in remote runtimes. It prevents unauthorized viewing with a full-screen UI lock page and blocks tool calls via `ctx.tools.guard` to prevent sensitive operations from being executed while locked. The plugin supports shared sessions, stores credentials encrypted with scrypt, and provides a server-side escape hatch. Note that it only protects the UI and process, not the HTTP API, and must be used together with network boundaries during deployment.