How do I configure TVA 19% + reverse-charge for EU B2B in Magento?

Romania has the following TVA rates:

• 19%, standard rate (most goods + services).
• 9%, reduced (food, books, restaurant meals, medical, water, hotel accommodation).
• 5%, super-reduced (residential housing under conditions, social housing, some cultural events, school books).

Magento configuration:

1. Create 3 tax classes in Stores → Tax Zones & Rates (TVA-19, TVA-9, TVA-5).
2. Create 3 tax rules per rate, scoped to RO destination.
3. Assign each product’s tax class based on its category (we wire this via a custom category_id → tax_class observer so admins don’t set it per product).
4. For EU B2B intra-community reverse-charge: override to 0% if a valid VIES-validated RO-prefixed CUI (or any EU TVA number) is on the customer.
5. For RO-domestic B2B: still 19% TVA but generate the e-Factura XML with the CUI on the invoice (mandatory).

Tax-inclusive prices on storefront (EU B2C rule); tax-exclusive on B2B if explicitly opted-in. Romania’s TVA threshold for compulsory registration is RON 300,000 turnover.