dsh-djy-xttsc: Global System Prompt Injection Plugin

The dsh-djy-xttsc plugin provides a visual “Big Fat Fish Instructions” configuration in the settings page to inject a global system prompt into all model requests. It supports hot reloading, persistent storage, and version compatibility, ensuring the instruction takes effect across sessions, workflows, and subagents. Installation requires command-line operations, while usage only involves enabling the option in the settings panel or modifying the instruction text. Note that the plugin content is injected as-is and conflicts with other injection sources in the same environment should be avoided. If the configuration does not take effect, enable diagnostic mode to troubleshoot.