- Add AdapterOutput type (stepHash, detailHash, role, frontmatter, body, startedAtMs, completedAtMs)
- Update FrontmatterFastPathResult to include frontmatter record
- Change createAgent to output JSON line instead of plain hash
- Update spawnAgent in cli-workflow to parse JSON
- Add adapter-stdout tests (A-group) and spawn-agent-json tests (B-group)