Add lithos-llm as a pinned git dependency and replace the in-repo
`test/twin/openai` crate with the published `twins` revision that
lithos-llm verifies its codecs against. Move the Fabro policy overlay
(`fabro-policy.toml`) into fabro-llm so Fabro owns its own catalog
policy layer.
Drop the twin-openai nextest overrides and CI package filter now that the
crate is no longer a workspace member.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
