dsh-diagon-alley: DeepSeek Harness Persona Switching Plugin

`dsh-diagon-alley` is a Host plugin that allows users to switch AI personas directly within DeepSeek Harness conversations. It supports flexible role switching by name, ID, or index, and provides features to view the role list and current status. Installation requires restarting `dsh web`, and users can operate it using natural language commands. Configuration supports two injection modes, `replace` and `append`, for replacing all prompts or appending to the end, respectively. Note that the role state is process-level, and variables must be properly registered to avoid errors.