feat(pr-review): add staged incremental pipeline

[Troublor]

Summary

• split PR review into deterministic prepare, compile, publish, and persist stages around schema-constrained Claude analysis
• persist a versioned manifest with reviewed SHAs, stable finding IDs, thread state, and full-versus-incremental routing
• add risk-based model and pre-mortem routing, compact message formats, atomic publication, stale-head protection, and internal-provenance suppression
• add unit coverage for manifest recovery, anchor handling, thread reconciliation, atomic review delivery, and stale-run behavior

Test plan

• mise run lint
• python3 -m unittest discover -s .github/actions/claude-pr-review -p "test_*.py" -v
• actionlint -shellcheck= .github/workflows/build-check.yml .github/workflows/claude.yml
• read-only preparation smoke test against megaeth-labs/documentation#84

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This PR was generated by an automated agent.

[github-actions]

Claude review status

✅ Review clean

Last reviewed: head 79a36be4

New this round: 0 · Resolved this round: 0 · Open questions: 0