docs(spec): clarify spec vs relay acceptance-criteria ownership

[sungjunlee]

Context

A review of the Acai/specsmaxxing discussion concluded that dev-backlog should not copy task-level acceptance criteria into durable spec/* artifacts. Task AC and frozen Done Criteria belong to GitHub/task files and dev-relay; spec-* owns durable project/system/capability contracts.

The current design mostly has this split, but the boundary is clearer in deep design docs than in the user-facing spec index and generated templates.

Desired change

Clarify the source-of-truth boundary in the small docs users and agents read first.

Suggested touchpoints:

• spec/README.md
• docs/spec-system-design.md
• skills/spec-grill/templates/capabilities.md
• skills/dev-backlog/references/integration-contract.md

Acceptance Criteria

• spec/README.md states that task AC stays in GitHub/task files, sprint execution context stays in backlog/sprints, and relay Done Criteria/rubrics/review stay in dev-relay.
• spec/capabilities.md template states that issue-specific AC, rubrics, and review notes do not live in capability specs.
• docs/spec-system-design.md records the rule: spec-* may read task AC as evidence, but must not copy task AC/Done Criteria into durable specs.
• integration-contract.md distinguishes task-file AC as mirror/local progress from relay run frozen Done Criteria as the review anchor.
• No new ACID/feature.yaml/dashboard/cross-link matrix is introduced.

[coderabbitai]

🔗 Related PRs

#100 - docs: spec-system v0.1 design (layered spec architecture) [merged]
#110 - docs: dogfood spec/capabilities.md for dev-backlog itself (#105) [merged]
#160 - [codex] split spec charter and grill skills [merged]
#174 - feat(backlog-triage): add spec-aware Decision Review [merged]

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