Add quality-gate-contract Chain Skill

[Dimon94]

Parent

#40

What to build

Add a Chain Skill that centralizes quality gate semantics shared by review, verification, simplification, and closeout. It should define finding severity, pass/fail/blocked verdicts, confirmed smell meaning, review escape rules, and which Failure Ledger entries become postmortem input.

This slice should include cc-simplify only at the quality gate level, not its full internal simplification workflow.

Acceptance criteria

• Quality Gate Contract defines review finding severity and advisory handling.
• It defines verification verdicts: pass, fail, and blocked.
• It defines confirmed smell semantics for simplification gates without importing the whole simplify workflow.
• It defines review escape eligibility for Failure Ledger writes.
• It defines closeout/postmortem input semantics for confirmed ledger entries.
• It does not duplicate workflow routing, task.md structure, or execution environment orchestration.
• Focused tests or contract checks prove the relevant quality skills can read it.

Blocked by

• Add skill-authoring-gate Chain Skill #41