Item 12: A necessity witness for every hypothesis that lacks one

Convention 2 asks for a necessity witness per hypothesis "where feasible". Rows in the frozen ledger that lack one, and where one is feasible, are contributable units: find the instance, display it, add the test.

Deliverable shape: witness-checked entries, one per hypothesis given a witness. Acceptance check: The witness checker accepts each instance.

Context: projects/normativity/consolidation-aug9/LEDGER.md, the necessity/sharpness column.