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>

prisma/migrations/20260610122819_drop_vat_from_offers_and_orders/migration.sql

@@ -0,0 +1,15 @@
+-- AlterTable
+ALTER TABLE `issued_order_items` DROP COLUMN `vat_rate`;
+
+-- AlterTable
+ALTER TABLE `issued_orders` DROP COLUMN `apply_vat`,
+    DROP COLUMN `vat_rate`;
+
+-- AlterTable
+ALTER TABLE `orders` DROP COLUMN `apply_vat`,
+    DROP COLUMN `vat_rate`;
+
+-- AlterTable
+ALTER TABLE `quotations` DROP COLUMN `apply_vat`,
+    DROP COLUMN `vat_rate`;
+

prisma/schema.prisma

@@ -347,8 +347,6 @@ model orders {
   status                String?          @default("prijata") @db.VarChar(30)
   currency              String?          @default("CZK") @db.VarChar(10)
   language              String?          @default("cs") @db.VarChar(5)
-  vat_rate              Decimal?         @default(21.00) @db.Decimal(5, 2)
-  apply_vat             Boolean?         @default(true)
   exchange_rate         Decimal?         @default(1.0000) @db.Decimal(10, 4)
   scope_title           String?          @db.VarChar(500)
   scope_description     String?          @db.Text
@@ -372,8 +370,6 @@ model issued_orders {
   supplier_id     Int?
   status          issued_orders_status @default(draft)
   currency        String?              @default("CZK") @db.VarChar(10)
-  vat_rate        Decimal?             @default(21.00) @db.Decimal(5, 2)
-  apply_vat       Boolean?             @default(true)
   exchange_rate   Decimal?             @default(1.0000) @db.Decimal(10, 4)
   order_date      DateTime?            @db.Date
   delivery_date   DateTime?            @db.Date
@@ -401,7 +397,6 @@ model issued_order_items {
   quantity         Decimal?      @default(1.000) @db.Decimal(12, 3)
   unit             String?       @db.VarChar(20)
   unit_price       Decimal?      @default(0.00) @db.Decimal(12, 2)
-  vat_rate         Decimal?      @default(21.00) @db.Decimal(5, 2)
   position         Int?          @default(0)
   issued_orders    issued_orders @relation(fields: [issued_order_id], references: [id], onDelete: Cascade, onUpdate: NoAction, map: "issued_order_items_ibfk_1")
 
@@ -494,8 +489,6 @@ model quotations {
   valid_until        DateTime?         @db.Date
   currency           String?           @default("CZK") @db.VarChar(10)
   language           String?           @default("cs") @db.VarChar(5)
-  vat_rate           Decimal?          @default(21.00) @db.Decimal(5, 2)
-  apply_vat          Boolean?          @default(true)
   order_id           Int?
   status             String            @default("active") @db.VarChar(20)
   scope_title        String?           @db.VarChar(500)