Stabilize mobile auth session handling

app/(app)/invoices/new.tsx

@@ -203,6 +203,15 @@ export default function NewInvoiceScreen() {
     setItems((prev) => prev.filter((_, i) => i !== index));
   }
 
+  function duplicateItem(index: number) {
+    setItems((prev) => {
+      const source = prev[index];
+      if (!source) return prev;
+      const copy = { ...source, id: undefined };
+      return [...prev.slice(0, index + 1), copy, ...prev.slice(index + 1)];
+    });
+  }
+
   function handleCreate() {
     if (!canCreate) return;
     setError(null);
@@ -327,6 +336,7 @@ export default function NewInvoiceScreen() {
                     isLast={index === items.length - 1}
                     onChange={(patch) => updateItem(index, patch)}
                     onRemove={() => removeItem(index)}
+                    onDuplicate={() => duplicateItem(index)}
                   />
                 ))}