Introduces CLA.md (individual CLA: contributors keep all rights to their
work, grant the project the right to offer contributions under additional
license terms; includes a written commitment in section 6 that the engine
remains open source) and a CLA Assistant Lite workflow that gates every PR
on a one-comment signature, with signatures stored in-repo on the
cla-signatures branch.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>