fix: harden review and verifier governance

scripts/review/partial_output_guard.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+STATUS_FILE="${1:?status file required}"
+CONTENT="$(cat "$STATUS_FILE")"
+
+if [[ "$CONTENT" != *'PARTIAL_OUTPUT_STATUS complete=false source=artifact-required conclusion=conservative'* ]]; then
+  echo "missing conservative partial-output template" >&2
+  exit 1
+fi
+
+echo "PARTIAL_OUTPUT_GUARD: PASS"