[GATE] x402 merchant onboarding + approval

[hasan-malik]

External dependency — kick off immediately.

Steps

1. Apply at https://x402-merchant.goat.network/ — pick a Merchant ID (e.g. `shieldclaw`), Name, email, password.
2. Sign the registration with your wallet (MetaMask).
3. DM @alicelliu on Telegram in the GOAT Builder Hub group with your Merchant ID — she approves applications.
4. Once approved, log in to the merchant portal.
5. Developer → Rotate API keys → save `API Key` + `API Secret`.
6. Settings → set receiving wallet address (where x402 sends payouts).
7. Paste into `.env`:
   • `GOATX402_API_URL=…`
   • `GOATX402_API_KEY=…`
   • `GOATX402_API_SECRET=…`
   • `GOATX402_MERCHANT_ID=…`
   • `GOATX402_RECEIVING_WALLET=…`
8. Test from the chat widget: `pay_finding` for an existing finding ID → should return a real tx hash.

Done when

• The agent's `pay_finding` tool fires a real USDC transfer on GOAT
• Tx visible on https://explorer.goat.network/

Why

This is submission gate #2. Judges explicitly test "trigger an automated machine payment in chat."