Record recovered fresh reviewer execution path

Changes: Document coordinator-authorized external readiness and successful post-release tool use through the shared reviewer/executor harness; add S00-016 evidence and handoff. No source or harness configuration changes.
Validation: Read-only readiness assertions passed with exit 0; tasks.py validate passed for 281 tasks at revision 29; git diff --check passed. Parent tasks remain blocked and unaccepted. Future provider capacity and S00-012 acceptance require separate fresh review.