DeepSeek Harness Plugin: dsh-rgate Remote Access Gateway

`dsh-rgate` is an identity authentication plugin for DeepSeek Harness that provides a full-page password wall, API restrictions, and session management for the Web UI. It addresses the security gap where `trustedHosts` only mitigates DNS rebinding rather than enforcing identity authentication, making login mandatory for non-loopback access. Core features include HMAC cookie authentication, login rate limiting, password audit logging, and scrypt-encrypted storage. Changes take effect after installation and a restart, making it suitable for enhancing security in self-hosted deployments.