Add LLM_API_KEY, LLM_BASE_URL, LLM_MODEL env vars so any OpenAI-compatible API (OpenRouter, etc.) can be used as the LLM backend without code changes.
Add LLM_API_KEY, LLM_BASE_URL, LLM_MODEL env vars so any OpenAI-compatible API (OpenRouter, etc.) can be used as the LLM backend without code changes.