Bug: item-selected refund limit excludes VAT (confirmed with Stripe, v2.0.0)

Hi team, please fix this refund-dialog inconsistency, reproduced on staging with FluentCart Core and Pro 2.0.0, EUR, tax-exclusive pricing and 21% VAT. All payments were Stripe sandbox tests, not live charges.

TL;DR: selecting the purchased item limits the refund to its pre-tax price, even though the selected transaction includes VAT.

Steps to reproduce:

1. Buy one item for €49 + €10.29 VAT = €59.29 using Stripe test mode.
2. Open the paid order and its refund dialog.
3. Select the charge and the purchased item.

Actual result: the transaction shows €59.29 paid, but the maximum refundable amount and refund button show only €49. Entering €59.29 is clamped back to €49 (screenshot attached).

Expected result: a full refund of the selected item should include its associated VAT, up to the remaining refundable transaction amount. Partial refunds should handle the corresponding tax consistently too.

Important workaround: removing the item selection changes the maximum to €59.29. We then refunded the entire €59.29 in ONE operation and verified the full refund in Stripe. So this is not a Stripe limitation, and two refunds are not inherently required. We also reproduced the item-selected limit with an offline test order (€10 + €2.10 VAT).

Please make the item-selected refund calculation and validation consistent with the amount actually paid, including VAT. Otherwise, following the default item-selected flow can leave the customer under-refunded. Thank you!