Function add_finding_entity 

pub fn add_finding_entity(
    path: &Path,
    finding_id: &str,
    entity_name: &str,
    entity_type: &str,
    reviewer: &str,
    reason: &str,
    apply: bool,
) -> Result<StateCommandReport, String>

v0.79: Append a new entity tag to an existing finding. Lands as a signed finding.entity_added event. Idempotent on (finding_id, entity_name): re-applying with the same name + type is a no-op so federation re-sync stays clean. Closes the v0.78.4 honest gap that forced reviewers to append new findings just to add a tag.