x402-paywalled demo API resource

DEMO-ONLY x402 (HTTP 402 Payment Required) resource mounted at the /api/v1 path that x402 scanners probe. A bare request returns HTTP 402 with an x402 accepts block pointing at a testnet wallet; a retry carrying an X-PAYMENT header returns a canned demo response. x402 discovery is inline in the 402 response, so this operation carries no x-payment-info. No settlement is verified. Forter does not sell goods or take real payment.