feat(vat)!: remove VAT entirely from offers, orders and issued orders

Accounting rule: nabidky, objednavky (incl. confirmation PDF) and objednavky
vydane are NOT tax documents - VAT belongs only on invoices. Per user
decision this is a FULL removal including DB columns.

- migration: DROP orders.vat_rate/apply_vat, issued_orders.vat_rate/apply_vat,
  issued_order_items.vat_rate, quotations.vat_rate/apply_vat (applied to
  dev + test DBs)
- services: net-only totals everywhere (computeIssuedOrderTotals(items) ->
  {total}; enrichOrder/enrichQuotation net; per-currency list totals net)
- PDFs (offers, order confirmation, issued order): no VAT columns/summary,
  single 'Celkem bez DPH' / 'Total excl. VAT' total, note under totals:
  'Ceny jsou uvedeny bez DPH. DPH bude uctovano dle platnych predpisu.';
  duplicate Cena/Celkem column merged (desc width 56%); orders-pdf render
  extracted as exported renderOrderConfirmationHtml for testability
- frontend: Uplatnit DPH checkboxes, VAT selects and per-item VAT columns
  removed from OfferDetail/OrderDetail/IssuedOrderDetail/
  OrderConfirmationModal/ReceivedOrders manual-create; list footers read
  'Celkem bez DPH'; invoice-from-order prefill now takes the company default
  VAT (invoice decides its own VAT)
- tests: suites reworked to net math; new pdf-vat-note.test.ts pins the
  exact cs+en note text and VAT-free layout on all three PDFs

Invoices and received invoices keep their VAT handling unchanged.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/admin/pages/InvoiceDetail.tsx

@@ -787,13 +787,12 @@ export default function InvoiceDetail() {
       }));
     }
 
-    // Pre-fill from order
+    // Pre-fill from order. Orders no longer carry VAT (not tax documents) —
+    // the invoice decides its own VAT: default rate from company settings,
+    // apply_vat on.
     if (fromOrderId && orderDataQuery.data) {
       const order = orderDataQuery.data;
-      const vatRate = numberOr(
-        order.vat_rate,
-        companySettings?.default_vat_rate ?? 21,
-      );
+      const vatRate = numberOr(companySettings?.default_vat_rate, 21);
       setForm((prev) => ({
         ...prev,
         customer_id: order.customer_id as number,
@@ -803,7 +802,7 @@ export default function InvoiceDetail() {
           (order.currency as string) ||
           companySettings?.default_currency ||
           "CZK",
-        apply_vat: Number(order.apply_vat) || 0,
+        apply_vat: 1,
         vat_rate: vatRate,
       }));
       const orderItems = order.items as Record<string, unknown>[] | undefined;