feat(conformance): add GenTech x402 gateway as reference example

[GentechLabs]

Summary

Adds a reference conformance example for the GenTech x402 payment gateway — a real, live, spec-compliant ARD manifest.

What this is

conformance/examples/gentech-x402/ard.json — a validated ARD manifest describing the GenTech x402 gateway (10 paid API services across Base, Solana, Avalanche, X Layer, Algorand, settled in USDC via the x402 protocol).

Why it's a good example

• Real, not synthetic — this is a live production gateway, not a mock. The manifest validates PASS against the v0.91 conformance CLI (0 critical errors, 0 warnings).
• Shows a paid/agent-economy resource — most existing examples are free public APIs (NOAA, local business). This demonstrates how a monetized agentic resource (x402 pay-per-call) is described in ARD, including metadata for settlement chains and service count.
• Uses the value-or-reference pattern — points at the live /.well-known/x402-bazaar manifest.

Verification

python3 conformance/bin/conformance-test manifest conformance/examples/gentech-x402/ard.json
# CONFORMANCE STATUS: PASS — 0 critical errors, 0 warnings

AI Disclosure

This PR was authored with assistance from an AI agent (Gentech). The manifest was validated against the project's own conformance CLI before submission. Human (Jordan) reviewed and approved.