The PoolReservationService already called PaymentRequestService::createRequest()
but with member_id=0 and payment_type='pool_reservation' — which was silently
rejected because 'pool_reservation' wasn't in the non-member whitelist.

- Added 'pool_reservation' to PaymentRequestService whitelist
- Added payment type label (حجز حارة سباحة)
- Added payment completion handler → marks reservation as paid
- Added void handler → reverts reservation to pending
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>