local config: add simplified LLM configuration

[howardjohn]

This allows starting with a config like:

llm:
  models:
  - name: claude-3-haiku
    provider:
      anthropic:
        model: claude-3-5-haiku-20241022
    params:
      apiKey: "$ANTHROPIC_API_KEY"
#    guardrails: ...
#    additionalHeaders: ...
  - name: thinking
    provider:
      anthropic: {}
    params:
      model: claude-sonnet-4-5-20250929
      apiKey: "$ANTHROPIC_API_KEY"

instead of a much more complex http-centric config.

A few things to figure out...

• Add support for guardrails, auth, etc
• Document/test how to mix the two modes (llm and binds)