feat(issued-orders): editable PDF heading 'Text objednavky (na PDF)' (order_text)

New nullable issued_orders.order_text column (migration applied to dev+test). The heading above the PDF items table is now editable per order, mirroring invoices' billing_text: empty falls back to the default, which is now 'Objednavame si u Vas:' per user wording. Field sits above Dodaci podminky in the detail form; persisted via create + update strFields (both schemas - the invoices Update-schema gap is not repeated). Tests: persistence round-trip incl. null-clears, PDF custom heading + default fallback.

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

src/routes/admin/issued-orders-pdf.ts

@@ -195,7 +195,7 @@ const translations: Record<Lang, Record<string, string>> = {
     buyer: "Odběratel",
     issue_date: "Datum vystavení:",
     delivery_date: "Požadované dodání:",
-    billing: "Objednáváme u Vás:",
+    billing: "Objednáváme si u Vás:",
     col_no: "Č.",
     col_desc: "Popis",
     col_qty: "Množství",
@@ -257,6 +257,8 @@ interface IssuedOrderPdfData {
   delivery_terms: string | null;
   payment_terms: string | null;
   issued_by: string | null;
+  // Editable heading above the items table; null → t.billing default.
+  order_text?: string | null;
 }
 
 interface IssuedOrderPdfItem {
@@ -771,7 +773,7 @@ ${indentCSS}
   </table>
 
   <!-- Polozky -->
-  <div class="billing-label">${escapeHtml(t.billing)}</div>
+  <div class="billing-label">${escapeHtml(order.order_text || t.billing)}</div>
   <table class="items">
     <thead>
       <tr>