Add Amazon PR/FAQ review handoff

[followdon]

Why

A clean Ringer delivery could reach the human review gate without a customer-led explanation of what changed, and an already-merged PR could be mistaken for a blocked current handoff. That made the final review package manual and made lifecycle language easy to overstate.

What changed

• Bundle an amazon-pr-faq skill with an Amazon Working Backwards template and deterministic evidence validator.
• Add two explicit modes:
  • review_handoff is the safe default and produces exactly READY or BLOCKED.
  • retrospective is explicit and records Built, Merged, Deployed, and Available separately for historical MERGED or CLOSED PRs.
• Hook every Ringer PR-facing handoff to $amazon-pr-faq in review_handoff mode. READY requires worker gates, full repository gates, fresh independent review, matching local/remote/GitHub head SHAs, mergeability, and successful required checks for the same commit. A later commit invalidates the package.
• Install and uninstall both bundled skill trees while preserving unrelated skills, hooks, and settings. Reinstallation removes stale files only inside Ringer-owned skill directories.
• Credit @followdon for the Amazon PR/FAQ handoff contribution.

Safety and authorization

The hook never pushes, creates or updates a PR, writes a PR body/comment, merges, or deploys merely to satisfy its gate. Missing authorization or evidence produces a BLOCKED package. The workflow stops at the human merge/deploy decision.

Verification

• Exact commit 02d00fa878a0bbde01a77df081268cdd3cab56ec: RINGER_HOME=/private/tmp/ringer-final-strict-exact-gates RINGER_NO_SELF_UPDATE=1 python3 -m unittest discover -s tests — 263 tests passed.
• RINGER_NO_SELF_UPDATE=1 python3 -m unittest tests.test_agent_install tests.test_amazon_pr_faq — 15 focused tests passed.
• python3 .claude/skills/amazon-pr-faq/scripts/validate_pr_faq.py --self-test — 8 valid scenarios accepted and 50 bad cases rejected.
• Bundled and installed skill validation — passed for both copies.
• Ringer adversarial verification — passed strict independent-review conclusions, full-SHA validation, phrase-local readiness/deployment negation, retrospective isolation, exact hook ownership, repository test discovery, and bundle/install parity.
• Fresh independent review of exact commit 02d00fa878a0bbde01a77df081268cdd3cab56ec — no actionable findings; 33 adversarial cases and the 263-test isolated suite passed.
• git diff --check — passed.
• Dogfood: CCS Dashboard PR #764 retrospective passed both the reusable evidence validator and a task-specific lifecycle checker.

No merge, deployment, or production operation is part of this PR.