DeepSeek Harness Plugin Manager

`relay-dsh-plugin-manager` is a standalone plugin designed for DeepSeek Harness (DSH), enabling full lifecycle plugin operations such as discovery, installation, updates, and management through a conversational interface. It supports secure change workflows (requiring confirmation before execution) and read-only queries, and integrates with the DSH Registry for plugin discovery. Users can easily search for, install, enable, or remove plugins using the `/plugins` command. Registry support defaults to HTTPS, and anonymous analytics can be optionally disabled. The plugin is compatible with DSH version 0.1.2.