dsh-trusted-host-is-loopback: Fixing Host-backed Setting Failures in Reverse Proxy Environments

The DeepSeek Harness (DSH) plugin `dsh-trusted-host-is-loopback` addresses issues where certain features fail when the authenticated Web UI is accessed through a reverse proxy because requests are incorrectly identified as remote. By modifying the client-side determination logic to mark the authentication page as a local loopback request, the plugin restores the availability of Host-backed settings (such as model configuration and API key settings) in reverse proxy scenarios. After installation, restart DSH; no additional configuration is required.