The claw402 gateway now settles chat routes pay-as-you-go (upto) and
reports the actual amount in the X-Claw402-Settled-Usd response header.
Capture it on all three x402 call paths (stream, simple, full), expose it
via Claw402Client.LastCallCostUSD, and prefer it over the flat catalog
estimate when recording ai_charges — cost stats now match real spend.