Local LLM

Document https://github.com/ollama/ollama and other opportunities for local/open model use.

Start by reviewing the guide's existing documentation structure and the linked Ollama project. Identify where guidance on local or open models belongs, then document Ollama and other relevant opportunities with enough context for macOS security and privacy readers. Done means the guide includes clear, useful coverage of the requested options.

Written by the indexing model from the issue text.