Fractal Provider Changes

Start Here

1. Inspect the current branch and worktree with git status --short; preserve unrelated user changes.
2. Read src/fractal/providers.py, src/fractal/onboarding.py, src/fractal/config.py, tests/test_providers.py, tests/test_cli_config.py, and README.md.
3. For model IDs, check current provider documentation or catalogs before editing. Do not rely on memory for active model names.
4. Decide whether the task is only a model-menu update or a new provider/runtime behavior.

Provider Registry Pattern

Most provider changes live in src/fractal/providers.py.