dsh-sovereign: Host-Plane Sovereignty Terms and Content Guard

`dsh-sovereign` is a host-plane plugin designed to resolve the conflict between agent behavior control and injection defense. It injects sovereign clauses into the system prompt to ensure the AI always complies with user-defined rules. Core features include user adjudication, external defense, dangerous operation adjudication, and tool result sanitization. v0.7.0 fixes the self-reference paradox, adopting the "who introduced it" determination standard. The plugin provides a four-state toggle for real-time monitoring of clause effectiveness, ensuring all sessions have defensive capabilities without requiring a specific mode to take effect.