238720e928
Replace the predicate unit test with an invariant on the real builder: a skill recorded by a foreground create is in build_learning_graph() with zero uses, and an unmarked never-used local skill is not. `hermes curator list-unmanaged` prints the actual marker (created_by:learn) instead of hard-coding created_by:null. Docs: curator.md and memory.md describe the learn marker and what the journey shows.