How do I configure KDV (Turkish VAT), 20% / 10% / 1% / 0%, by category?

Türkiye has four standard KDV rates, raised in 2023 (from 18% → 20% etc.):

• 20%, standard rate (most goods + services).
• 10%, reduced (textile + apparel, basic food, books, transport, restaurants).
• 1%, super-reduced (basic groceries, milk/bread/grain, newspapers, agricultural products).
• 0%, exempt (exports, intra-Customs-Union with EU under certain conditions, gold/silver bullion, some education + healthcare).

Magento configuration:

1. Create 4 tax classes in Stores → Tax Zones & Rates (KDV-20, KDV-10, KDV-1, KDV-0).
2. Create 4 tax rules per rate, scoped to TR (or destination-based if exporting).
3. Assign each product’s tax class based on its GTIP code (Turkish customs classification), we wire this via a category_id → tax_class mapping observer.
4. For exports: 0% KDV with proper customs documentation (Gümrük Çıkış Beyannamesi); the export-mode override is detected from shipping country.
5. Tax-inclusive prices on storefront (mandatory in TR retail); KDV breakdown displayed on the e-Fatura / e-Arşiv invoice line items.