fix(ui): guard delete on paid invoices / ordered-or-locked offers; add guarded delete to issued orders

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

src/admin/pages/OfferDetail.tsx

@@ -663,6 +663,11 @@ export default function OfferDetail() {
   const isLockedByOther = !!lockedBy;
   const readOnly = isInvalidated || isLockedByOther || isCompleted;
   const canInvalidate = isEdit && !isInvalidated && !isCompleted && !orderInfo;
+  // An offer is deletable only when it has NOT spawned an order (orderInfo —
+  // deleting would orphan the linked order), is NOT invalidated, and is NOT
+  // locked by another user. (Backend rejection of deleting an ordered offer is
+  // a separate hardening, out of scope here.)
+  const canDelete = isEdit && !orderInfo && !isInvalidated && !isLockedByOther;
 
   // Sync offer detail data to form state on first load (edit mode)
   const formInitializedRef = useRef(false);
@@ -1190,7 +1195,7 @@ export default function OfferDetail() {
                 {saving ? "Ukládání..." : "Uložit"}
               </Button>
             )}
-            {isEdit && hasPermission("offers.delete") && (
+            {canDelete && hasPermission("offers.delete") && (
               <Button
                 onClick={() => setDeleteConfirm(true)}
                 variant="outlined"