[zkVM] Ψ on-chain computation — RISC Zero / Nexus / SP1 #2

Integrate the Meta-Bell Ψ statistic into a zkVM backend.

Goal: prove validator independence on-chain without
revealing what was validated.

Candidates: RISC Zero, Nexus, SP1

Scope:

• Evaluate zkVM backends for Ψ computation
• Implement proof generation
• Benchmark proof size and verification time

Reference: docs/math.md, Bell-SPVU paper (DOI: 10.5281/zenodo.19656679)
Difficulty: Advanced
Phase: 3