feat(issued-orders): make line items optional (issue by sections alone)

Items are no longer required on issued orders — an order can be issued
purely from its rich-text sections (Obsah).

- DocumentItemsEditor: opt-in allowEmpty prop lets the list go to zero
  rows (default false keeps the offers/invoices at-least-one-item rule).
- IssuedOrderDetail: allowEmpty on the editor; a saved order with no
  items reopens empty (not a blank starter row); submit guard now
  requires at least one item OR a non-empty section, not an item.
- PDF: with no items the billing heading, items table and total row are
  omitted entirely — a sections-only order shows only its Obsah.
- Service: finalize (draft->sent) and create-as-non-draft reject a
  completely blank order (no items AND no sections) with a Czech 400
  (empty_document); drafts may still be saved empty as WIP.
- Tests: sections-only finalize + blank-order rejection + sections-only
  PDF render; existing finalize fixtures given minimal content.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/components/document/DocumentItemsEditor.tsx

@@ -492,6 +492,12 @@ interface DocumentItemsEditorProps {
   itemDescriptionMaxLength?: number;
   /** Optional page-specific control (e.g. item-template Select) next to the add button. */
   templatesSlot?: ReactNode;
+  /**
+   * Allow removing every row so the list can be empty (issued orders may be
+   * issued by sections alone). Default false keeps the offers/invoices rule of
+   * at least one item.
+   */
+  allowEmpty?: boolean;
 }
 
 /**
@@ -509,6 +515,7 @@ export default function DocumentItemsEditor({
   showDiscount = false,
   itemDescriptionMaxLength = 5000,
   templatesSlot,
+  allowEmpty = false,
 }: DocumentItemsEditorProps) {
   const theme = useTheme();
   const isMobile = useMediaQuery(theme.breakpoints.down("sm"));
@@ -538,10 +545,13 @@ export default function DocumentItemsEditor({
   const addItem = () => onChange([...items, emptyDocumentItem()]);
 
   const removeItem = (index: number) => {
-    if (items.length <= 1) return;
+    if (!allowEmpty && items.length <= 1) return;
     onChange(items.filter((_, i) => i !== index));
   };
 
+  // When allowEmpty, even the last row is deletable (list may go to zero).
+  const canDeleteRow = allowEmpty || items.length > 1;
+
   const handleDragEnd = (event: DragEndEvent) => {
     const { active, over } = event;
     if (!over || active.id === over.id) return;
@@ -608,7 +618,7 @@ export default function DocumentItemsEditor({
                   index={index}
                   currency={currency}
                   readOnly={readOnly}
-                  canDelete={items.length > 1}
+                  canDelete={canDeleteRow}
                   showIncludedInTotal={showIncludedInTotal}
                   showDiscount={showDiscount}
                   itemDescriptionMaxLength={itemDescriptionMaxLength}
@@ -666,7 +676,7 @@ export default function DocumentItemsEditor({
                       index={index}
                       currency={currency}
                       readOnly={readOnly}
-                      canDelete={items.length > 1}
+                      canDelete={canDeleteRow}
                       showIncludedInTotal={showIncludedInTotal}
                       showDiscount={showDiscount}
                       itemDescriptionMaxLength={itemDescriptionMaxLength}