dsh-auth-gate: An Authentication Gate Plugin for DeepSeek Harness

`dsh-auth-gate` is a security plugin for DeepSeek Harness (DSH), designed to provide login authentication and protection for the Web UI. It intercepts unauthenticated requests upfront through the Nginx `auth_request` interface and offers core features such as SVG image CAPTCHA, brute-force protection (with IP and account rate limiting), single sign-on, and encrypted password storage. The plugin listens on localhost by default and must be configured through an Nginx reverse proxy. After the first login, changing the default credentials is mandatory. To ensure security, public-facing deployments should use HTTPS.