Add Signum — contract-first dev pipeline with 3-model audit

[t3chn]

Plugin: heurema/signum
Category: Code Quality / Development Pipeline

Contract-first development pipeline for Claude Code. Spec quality grading → multi-model audit (Claude + Codex + Gemini) → tamper-evident proofpack.json.

Features: holdout scenarios (blind testing), iterative fix loop (up to 20 iterations), anti-entropy cleanup contracts, SOC2-ready attestation.

Install: claude plugin marketplace add heurema/emporium && claude plugin install signum@emporium