dsh-plugin-login-gate: Add Password Login and HTTPS Reverse Proxy to DeepSeek Harness

The DeepSeek Harness (dsh) plugin adds a password login gate and an HTTPS reverse proxy to the Web UI, addressing the security and compatibility issues caused by the default loopback-only access and cross-device LAN access. It supports single-password login, self-signed certificate encryption, automatic protocol redirection, and full forwarding of streaming output. For LAN access, the plugin fixes issues such as 403 errors, an unavailable settings page, and WebSocket handshake failures by rewriting the Host header and applying patches to support non-loopback IP addresses. To use it, configure the password file, generate the certificate, and restart the service. Note that the password is stored in plaintext, and `lanPatch` modifies the dsh source code; after updates, the patch script must be re-run.