feat(issued-orders): counterparty is now a supplier (dodavatel), not a customer

Issued orders are purchase orders WE send - they must pick from suppliers
(sklad_suppliers), not from customers. Per user decision customer_id was
REPLACED (not kept alongside): migration drops issued_orders.customer_id and
adds supplier_id FK -> sklad_suppliers (existing rows lose their counterparty
- the feature is days old; re-point them in the UI).

- service: input/filters/search (suppliers.name + ico)/enrichment/detail all
  supplier-based; create validates the supplier inside the transaction and
  update before write -> Czech 400 'Dodavatel nenalezen' instead of P2003 500;
  detail returns a minimal supplier field set (no internal notes leak)
- routes: supplier_id on list + stats; new GET /issued-orders/suppliers
  lookup (orders.view/create/edit guard - orders users lack warehouse.manage
  which guards the warehouse suppliers CRUD), active suppliers only,
  name+id ordering
- PDF: Dodavatel block now renders the supplier (name, newline-split address,
  IC/DIC), layout and both language label sets unchanged
- frontend: new SupplierPicker kit component (CustomerPicker untouched),
  IssuedOrderDetail/IssuedOrders switched to supplier_id/supplier_name; the
  picker keeps a fallback option for orders whose supplier was later
  deactivated; WarehouseSuppliers CRUD now also invalidates issued-orders so
  the picker can't go stale
- tests: issued-orders suite switched to supplier fixtures + new coverage
  (lookup shape + 403, nonexistent supplier 400, PDF supplier block)

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

prisma/migrations/20260610104514_issued_orders_customer_to_supplier/migration.sql

@@ -0,0 +1,16 @@
+-- DropForeignKey
+ALTER TABLE `issued_orders` DROP FOREIGN KEY `issued_orders_ibfk_1`;
+
+-- DropIndex
+DROP INDEX `issued_orders_customer_id` ON `issued_orders`;
+
+-- AlterTable
+ALTER TABLE `issued_orders` DROP COLUMN `customer_id`,
+    ADD COLUMN `supplier_id` INTEGER NULL;
+
+-- CreateIndex
+CREATE INDEX `issued_orders_supplier_id` ON `issued_orders`(`supplier_id`);
+
+-- AddForeignKey
+ALTER TABLE `issued_orders` ADD CONSTRAINT `issued_orders_supplier_fk` FOREIGN KEY (`supplier_id`) REFERENCES `sklad_suppliers`(`id`) ON DELETE RESTRICT ON UPDATE NO ACTION;
+