Adds ai::config: one serde struct for every LLM setting (backend, llama.cpp,
Ollama, OpenRouter, embedding, TTS, agentic caps), resolved as defaults ->
llm.toml (LLM_CONFIG_PATH, default ./llm.toml) -> the old env vars. Env
overrides are kept for one release and listed in a single startup
deprecation warning; LLAMA_SWAP_ALLOWED_MODELS maps to picker.include so
current deploys keep their picker. Unknown keys, zero timeouts and
backend=llamacpp without a URL fail startup. OPENROUTER_API_KEY stays
env-only.
llm.example.toml documents the schema and is parsed by a test. main loads
the config right after tracing init; readers switch over next.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
