Settles a verified x402 payment on-chain (broadcasts the transfer, confirms it, and records a ledger entry), returning the settlement result with an on-chain transaction reference. The body takes the signed payment plus optional feeQuoteId, reference, and shielded; for upto payments, pass settledAmount to charge less than the signed cap. For batch-settlement payments the call returns 202 Accepted with settled: false and a batchId instead of settling immediately. Requires a signed Authorization header (and an X-Payment x402 header when settling a 402-gated resource).