dsh-mcp-center: Connect MCP Server in DeepSeek Harness Settings

`dsh-mcp-center` is a plugin designed for the DeepSeek Harness `web` profile, used to register and manage MCP servers within the settings page. It supports both Streamable HTTP remote endpoints and local stdio servers, featuring a built-in MCP client transport that eliminates the need for external SDKs. Users can configure server information via the `Settings → MCP Center` page, including HTTP authentication modes (None, Bearer token, Custom headers) or stdio parameters (such as command and environment variables). Upon saving the configuration, the connection is established immediately, and tools are made available to the model in the format `mcp__<name>__<tool>`. The configuration is saved locally at `~/.dsh/mcp-cente`.