Wise Payouts

- SECURITY: Webhook signature verification now fails CLOSED. Previously, if no webhook public key was configured — or if the cryptography library was unavailable — verification returned success, allowing an attacker to forge transfer status events. It now rejects the webhook in both cases. ACTION REQUIRED: configure the Webhook Public Key to continue receiving Wise webhook status updates.
- SECURITY: Webhook replay protection. Events whose signed 'sent_at' timestamp is outside a 5-minute window are now rejected, so a captured valid webhook can no longer be replayed indefinitely.
- SECURITY: Transfer creation now requires a stable external_id as the Wise customerTransactionId (idempotency key) instead of falling back to a random per-call UUID. This prevents a retry after a lost/timed-out response from creating and funding a second transfer (double payout).
- Funding failures are no longer swallowed. If a transfer is created but funding from balance fails, the payout is reported as failed ('created_unfunded') with the transfer id for reconciliation, instead of being recorded as a successful payout that never moved money.
- On retry, transfers that Wise already returns as funded/processing are no longer re-funded.
- Money amounts are quantized to the currency's minor units and sent as exact JSON numbers instead of via float(), fixing binary floating-point rounding errors (including correct handling of zero-decimal e.g. JPY and three-decimal e.g. KWD currencies).

- Initial release
- Single transfer support via Wise API
- Bearer token authentication
- Quote-based transfers with real exchange rates
- Webhook signature verification
- Sandbox and Production environment support