[EPIC] RC2: Cryptographic Hardening


**Epic Goal:** Upgrade cryptographic primitives to production standards.

**Scope:** Replace mock/hash-based crypto with ECVRF and CLSAG ring signatures. 

**Success Criteria:**
- ✅ ECVRF provides verifiable randomness
- ✅ CLSAG ring signatures enable privacy
- ✅ Key image tracking prevents double-signing
- ✅ All primitives pass security review

**Dependencies:** Requires RC1 crypto foundation
        