dsh-opencode-patch: Make OpenCode Models Available in the DeepSeek Harness

`dsh-opencode-patch` is a plugin designed specifically for DeepSeek Harness to fix the issue where the OpenCode model fails to work under its default configuration. By restoring session affinity, gateway source headers, and providing tool definitions for the free tier, it resolves request rejections caused by missing network-layer protocol support. Additionally, the plugin supports offline caching of model catalogs and a real-time billing dashboard, ensuring that traffic from other providers remains unaffected.