Add Sign in with Grok mirroring the merged ChatGPT/Codex integration: a strix/config/grok.py OAuth module (PKCE loopback flow against auth.x.ai, refresh with cross-process locking, secure ~/.strix/subscription-auth.json store) plus grok/<model> routing through the OpenAI-compatible api.x.ai/v1 endpoint via a bearer-stamping chat-completions client.
strix auth login grok / status / logout become provider-aware; subscription.py shares provider-agnostic auth-mode detection; Grok runs are marked zero-cost like other subscriptions.
Uses a consumer subscription outside xAI own products, which xAI does not officially support; opt-in and experimental.