feat: unify review/triage verdict reporting on a shared JSON contract

Changed

• The reviewer and triage agents now report their verdict as a fenced json block
  ({"branch", "slug", "verdict", "detail", "findings"} / {"fixable", "category", "detail"})
  instead of column-0 ## Branch:/AC:/Review:/FINDING: and FIXABLE:/CATEGORY:/DETAIL:
  lines, mirroring the structured-result contract crew-coder already used. The old shape had
  three independent hand-rolled parsers of the same aggregate review report file — a Node regex
  gating the merge, an awk in crew-summary.sh's rollup, and a second awk in
  promote-findings.sh's remind — and they drifted apart on how much whitespace a
  herdr-captured review header could carry before a line no longer matched. A genuinely
  successful, all-met retry review could land indented and without the ## after an earlier
  not_run stub in the same file and still be silently dropped from the summary and the findings
  count, even though the merge/AC gate (whose regex already tolerated leading whitespace) had
  parsed and acted on the real verdict correctly. JSON's whitespace-between-tokens-is-insignificant
  grammar closes the whole class rather than one more anchor at a time — crew-summary.sh and
  promote-findings.sh now both read the aggregate file through one shared parser
  (orchestrator/review-rollup.mjs, over report.mjs's new parseReviewAggregate) instead of
  reimplementing it twice. report.mjs's parseReviewReport/parseTriageReport prefer the json
  block and fall back to the old markdown shape, so an un-migrated reviewer/triage agent still
  works. mark-not-run's stub now emits the same json shape (verdict: "not_run").