governance_coding institutional edge invariant

Trap: an institutional final class with empty power_changes looks conservative when evidence proves policy text but no defensible actor/right edge. Fix: effective_institutional_change, announced_institutional_change, and proposal_only always require a nonempty, quote-grounded edge with matching status and dates; otherwise revise to control_event/no_event or abstain. Schema-valid shape alone is insufficient because semantic validation enforces the power-graph ontology.