Automate PR review preflight and thread response flow

[JamesCarnley]

Summary

The PR/review process is documented and working, but still relies on humans/agents remembering too much ceremony.

This issue tracks the highest-leverage helper tooling to make clean PR review the default instead of a prompt-quality accident.

Scope

• Add scripts/review/preflight-pr
• Add scripts/review/respond-threads (or equivalent)
• Add yarn review:check

Desired behavior

scripts/review/preflight-pr

Produce one review briefing that gathers:

• PR description
• Agents involved
• changed files
• unresolved review threads
• existing agent-authored review comments
• likely governing specs / ADRs for the touched area

scripts/review/respond-threads

Support the review-response-manager flow with:

• unresolved thread pagination
• fixed / pushback / future-work classification support
• native review-thread replies
• GraphQL thread resolution
• retries / failure handling
• dry-run mode before mutating thread state

yarn review:check

Lightweight local validation for:

• PR template completeness
• [model · role] prefix format
• thread-response metadata / hygiene

Why

This was identified as the best next step after PR #10. The process is good, but operational friction still causes drift.

References

• docs/HUMAN_PR_WORKFLOW.md
• docs/review/review-squad.md
• docs/agent-workflow.md
• docs/FUTURE_WORK.md → Tooling & Process