fix preview inputs and markup preview

frontend/src/nodeWidgetDefaults.js

@@ -0,0 +1,26 @@
+import { DATA_TYPES } from './constants.js';
+
+export function getDefaultWidgetValue(spec) {
+  const [type, opts] = Array.isArray(spec) ? spec : [spec, {}];
+  if (DATA_TYPES.has(type)) return undefined;
+  if (type === 'BUTTON') return undefined;
+  if (Array.isArray(type)) {
+    if (typeof opts?.default === 'string' && type.includes(opts.default)) {
+      return opts.default;
+    }
+    return type[0];
+  }
+  return opts?.default ?? '';
+}
+
+export function buildDefaultWidgetValues(definition) {
+  const widgetValues = {};
+  const required = definition?.input?.required || {};
+  for (const [name, spec] of Object.entries(required)) {
+    const value = getDefaultWidgetValue(spec);
+    if (value !== undefined) {
+      widgetValues[name] = value;
+    }
+  }
+  return widgetValues;
+}