dsh-plugin-manager: DSH Web Plugin Management Plugin

`dsh-plugin-manager` is a Web management plugin for DeepSeek Harness (DSH), designed to replace cumbersome manual configuration with a graphical interface for intuitive plugin toggling. It supports hot reloading, automatically persists state to `cordis.patch.yml`, and provides search filtering, status display, and security protections (trusted request fence and core protection). The plugin is restricted to loopback-address access only, and write requests are subject to size limits.