Apply a Self-Hosted state transition

Applies one Self-Hosted state transition, discriminated by action: save a mode's config (no on/off or active-mode change), activate a mode (enable Self-Hosted and route calls through it — enable or switch), or disable. Each mode (llm/audio) has its own independent config.

The signing secret for a mode is minted the first time you save a wsUrl for it. Retrieve it from GET /api/v1/self-hosted/secret?mode=… and set up your server's X-Dial-Signature verification before you activate (activating routes your calls at the server immediately). Returns the full configuration after the change.