v0.11.0 - sanctions screening

Added

• Sanctions screening (live since 7 October 2026): error codes PAYER_SANCTIONED (action
  STOP_SUBSCRIPTION - stop charging that subscription) and RECIPIENT_SANCTIONED (action
  INVALID_REQUEST - the receiving wallet is on the OFAC list; retrying gives the same answer).
  Nothing was submitted when either is returned. Show buyers a neutral message such as "This wallet
  cannot be used with P2Flux. No transaction was submitted." (https://p2flux.com/docs/errors.html#sanctions)
• verifyPayment() passes through screening: 'clear' | 'sanctioned' | 'unknown' (documented in the
  return shape).