dsh-inject-system-prompt: Inject a System Prompt into the DeepSeek Harness Agent

The DeepSeek Harness plugin `dsh-inject-system-prompt` is designed to address the inflexibility of modifying the main configuration when customizing the behavior of specific agents. Through the `ctx.systemPrompt.section()` registration mechanism, it allows users to inject custom content into the system prompt in the form of a configuration bundle. Users must have Node.js 22.19+ or 24+ installed and install the plugin via pnpm. During configuration, the plugin must be activated and parameters such as `text` must be set, supporting the customization of the prompt text, name, ordering, and override mode to achieve more flexible control over agent behavior.