Add GetVATConfig for reading VAT settings via any db.Querier, ApplyVATToBookingPayment for applying VAT to payment records, and ApplyVATToTillSale for SPV gift card till sales. Errors are logged without blocking payment flow. Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent) Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>