Global config for sai-cli lives at:
- Linux: ~/.config/sai/config.yaml
- macOS: ~/Library/Application Support/sai/config.yaml
- Windows: %APPDATA%/sai/config.yaml

Sections:
- ai: provider (openai|azure), credentials, model, and optional base URL/endpoint.
  Env vars override file values: SAI_PROVIDER, SAI_OPENAI_API_KEY/BASE_URL/MODEL,
  SAI_AZURE_API_KEY/ENDPOINT/DEPLOYMENT/API_VERSION.
- default_prompt: meta_prompt plus tools[]. Used whenever you omit a per-call
  prompt YAML. Provide a prompt file as the first argument to override.
- history: optional customization for log path/rotation if you differ from defaults.

`sai --init` writes a starter config with placeholder credentials and a built-in
set of everyday tools. Environment variables are the quickest way to swap models
or providers per shell without editing the file.
