[TODO] License scanning (REUSE compliance)

From TODO.md: Add license scanning/REUSE compliance checks to clarify licensing and prevent incompatible additions.

Start with the entry in TODO.md and inspect how this repository currently runs automated checks. Determine where a REUSE or license-scanning check would belong and what license violations it must catch. Done means the project has an automated compliance check that prevents incompatible additions.

Written by the indexing model from the issue text.