epic(backlog-triage): add spec-aware Decision Review

[sungjunlee]

Problem

backlog-triage currently surfaces useful signals (classification, relationships, stale candidates, priority and milestone proposals), but it does not make the final editorial call: which open issues are worth doing now, which need shaping, which should wait, and which should be dropped.

Goal

Add a lightweight, report-only Decision Review layer that uses the current spec system as evidence:

• spec/charter.md for direction, Objectives, and Non-Goals
• spec/capabilities.md for capability fit, scope, and hard constraints
• spec/system-map.md when present for high-level boundary contradictions
• active sprint context for timing and in-flight protection
• the issue snapshot / relationships / stale signals for backlog evidence

The report should help a maintainer quickly choose the next sprint candidates and cleanup actions.

Non-goals

• Do not make spec files mandatory; absence must degrade gracefully.
• Do not mutate spec/ artifacts from backlog-triage.
• Do not add new GitHub mutation verbs in the first pass.
• Do not turn backlog-triage into a lifecycle workflow engine.

Child issues

• docs(backlog-triage): resolve spec-charter naming and charter path fallback #168 docs(backlog-triage): resolve spec-charter naming and charter path fallback
• docs(backlog-triage): define Decision Review rubric #169 docs(backlog-triage): define Decision Review rubric
• docs(backlog-triage): add capability-fit guidance from spec/capabilities.md #170 docs(backlog-triage): add capability-fit guidance from spec/capabilities.md
• docs(backlog-triage): include optional spec/system-map boundary check #171 docs(backlog-triage): include optional spec/system-map boundary check
• enhance(backlog-triage): add Decision Review to the report contract #172 enhance(backlog-triage): add Decision Review to the report contract
• test(backlog-triage): dogfood Decision Review on dev-backlog open issues #173 test(backlog-triage): dogfood Decision Review on dev-backlog open issues

[coderabbitai]

🔗 Related PRs

#74 - feat(backlog-triage): triage report renderer (#64) [merged]
#100 - docs: spec-system v0.1 design (layered spec architecture) [merged]
#106 - docs(backlog-charter): create-mode interview + signals + seed-Decisions guidance (#93 #94 #96) [merged]
#110 - docs: dogfood spec/capabilities.md for dev-backlog itself (#105) [merged]
#160 - [codex] split spec charter and grill skills [merged]

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[sungjunlee]

Completed #168-#173. Local docs now define spec-aware Decision Review, dogfood report was generated at backlog/triage/2026-05-31-decision-review-dogfood.md, and CI-equivalent checks passed: node --test skills//scripts/.test.js and bash skills/dev-backlog/scripts/smoke-test.sh.