Payment manifest for x402: payable endpoints, network, asset and tier prices (404 when x402 is not enabled)

Lists every endpoint that accepts an x402 payment, with the network, asset, receive address and tier prices, so an agent that knows only the domain can price the whole surface before paying. Generated from the same code that renders a live 402 challenge, so the two cannot disagree. Returns 404 on a deployment that does not accept x402. Unauthenticated, free and unmetered.