pass a copy when opening dialog

otherwise, any changes the dialog makes will reflect in the calling
view's object

dashboard/src/components/UserDialog.vue

@@ -179,6 +179,7 @@ async function onSubmit() {
 
 defineExpose({
   async open(u = null) {
+    u = u ? JSON.parse(JSON.stringify(u)) : null; // make a copy
     busy.value = false;
     formError.value = {};
     user.value = u;