Add Revettr counterparty risk scoring skill

[AlexanderLawson17]

Summary

• Adds skills/revettr/ with SKILL.md routing table and two reference docs
• setup.md: endpoint discovery, x402 payment flow, free tier (skip_insumer), supported entity types and chains
• risk-check.md: /v1/score (risk scoring), /v1/attest (JWS signed attestation), /v1/batch (batch scoring), score tiers, flags, signal breakdown, and a pre-send integration pattern

Revettr scores counterparty risk (0 to 100) for wallets, domains, IPs, and company names before agents send funds. It checks on-chain signals (tx count, wallet age, counterparty diversity), off-chain data (WHOIS, geolocation, OFAC/EU/UN sanctions), and cross-chain trust profiles via InsumerAPI. TWAK already speaks x402, so agents can call Revettr with zero additional auth setup.

Structure

skills/revettr/
├── SKILL.md                    # Routing table (matches existing skill format)
└── references/
    ├── setup.md                # Discovery, tiers, x402 payment, curl examples
    └── risk-check.md           # Score, attest, batch endpoints + pre-send pattern

Test plan

• Verify SKILL.md frontmatter parses correctly (name + description fields)
• Verify routing table links resolve to the correct reference files
• Confirm curl and twak examples work against the live Revettr API
• Confirm free tier works with skip_insumer=true (no payment required)