Align findings schema with PR #2 trust-boundary semanticsVerified

PR #2 made repo-controlled files advisory-only but touched prompts only,
leaving the schema out of step:

- Add optional policy_dispute field to true_positive so the
  disputed-by-policy annotation from gates.md rule 0 has a home in
  findings.json (additionalProperties: false would have rejected it).
- reproducer.status "ran" no longer described as "against the real
  build" — s6b now forbids running the target's build or harness.
- false_positive entries described as advisory prioritization signal,
  not "so a later run doesn't re-litigate" suppression state.
- SKILL.md s9 points the model at the new field.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>