Add openfang-rail (remote MCP: deterministic identity & rental checks, x402 per-call payments)

[89rat]

What

Adds openfang-rail as a remote MCP server entry (type: remote, streamable-http).

• URL: https://rail.akrivis.in/mcp — standard MCP JSON-RPC 2.0 (initialize / tools/list / tools/call), no OAuth, no headers, dynamic tool discovery.
• What it does: 28 deterministic tools — business-identity validation (IBAN, LEI, VAT, UK company number, ISIN, EAN-13, GSTIN), rental due-diligence (deposit-safety, listing-risk), and on-chain lookups — every result ships with a signed XDR-1 receipt that verifies offline.
• Auth/pricing: free tier per day per client, no signup. Beyond it, calls are paid per request via x402 (gasless EIP-3009 USDC on Base, non-custodial) — entirely transparent to an MCP client that doesn't pay (it just sees the free tier / 402 challenge on exhausted tools).
• Source: https://github.com/89rat/openfang-rail (MIT). The repo also contains a Dockerfile + zero-dependency stdio↔HTTP bridge, so the server can be consumed local-container style as well.

Verification

• initialize → serverInfo: openfang-rail; tools/list → 28 tools (verified against the live endpoint today).
• No test credentials needed: no secrets, no config — the entry has an empty config surface by design.