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>

src/admin/ui/SupplierPicker.tsx

@@ -0,0 +1,88 @@
+import Autocomplete, { createFilterOptions } from "@mui/material/Autocomplete";
+import MuiTextField from "@mui/material/TextField";
+import Box from "@mui/material/Box";
+import Typography from "@mui/material/Typography";
+import type { Supplier } from "../lib/queries/issued-orders";
+
+interface SupplierPickerProps {
+  suppliers: Supplier[];
+  /** Selected supplier id (FK), or null when none chosen. */
+  value: number | null;
+  onChange: (id: number | null) => void;
+  disabled?: boolean;
+  /**
+   * When set, draws the input in its error state (red border). The error TEXT
+   * is owned by the surrounding <Field> wrapper, so we deliberately do NOT
+   * render helperText here to avoid duplicating the message.
+   */
+  error?: string;
+  placeholder?: string;
+  /** Optional id forwarded by <Field> for label association. */
+  id?: string;
+}
+
+// Search matches the supplier name AND the IČO, so typing either finds the
+// record. Match on a stringified "name + ico" so MUI's default
+// case-insensitive substring filtering covers both.
+const filterSuppliers = createFilterOptions<Supplier>({
+  stringify: (s) => `${s.name} ${s.ico ?? ""}`,
+});
+
+/**
+ * Searchable supplier picker for issued orders (purchase orders) — a
+ * controlled MUI Autocomplete over the sklad_suppliers lookup list, bound to
+ * the supplier id. Modeled on CustomerPicker (offers/invoices keep that one);
+ * renders bare (no label/error text); wrap it in the page's
+ * <Field label error> for the label + error line.
+ */
+export default function SupplierPicker({
+  suppliers,
+  value,
+  onChange,
+  disabled,
+  error,
+  placeholder,
+  id,
+}: SupplierPickerProps) {
+  const selected = suppliers.find((s) => s.id === value) ?? null;
+  return (
+    <Autocomplete<Supplier>
+      options={suppliers}
+      value={selected}
+      onChange={(_, opt) => onChange(opt ? opt.id : null)}
+      getOptionLabel={(s) => s?.name ?? ""}
+      isOptionEqualToValue={(o, v) => o.id === v.id}
+      filterOptions={filterSuppliers}
+      disabled={disabled}
+      size="small"
+      fullWidth
+      autoHighlight
+      renderOption={(props, s) => {
+        const { key, ...rest } = props as typeof props & { key: string };
+        return (
+          <Box component="li" key={key} {...rest}>
+            <Box>
+              {s.name}
+              {s.ico && (
+                <Typography
+                  variant="caption"
+                  sx={{ display: "block", color: "text.secondary" }}
+                >
+                  IČ: {s.ico}
+                </Typography>
+              )}
+            </Box>
+          </Box>
+        );
+      }}
+      renderInput={(params) => (
+        <MuiTextField
+          {...params}
+          id={id}
+          placeholder={placeholder ?? "Vyberte dodavatele…"}
+          error={!!error}
+        />
+      )}
+    />
+  );
+}