New jarvis-core::llm module providing a blocking client for
OpenAI-compatible chat completions endpoints (Groq by default).
- LlmClient::new / from_env (GROQ_TOKEN, GROQ_BASE_URL, GROQ_MODEL)
- complete(messages, max_tokens) -> String
- thiserror-based LlmError / ConfigError
- gated behind a new llm feature, included in default jarvis_app
Not yet wired into the wake-word/intent loop; that lands in v0.3.
