feat: add questionnaire definitions and their catalog

src/Enum/ChoiceWidget.php

@@ -0,0 +1,12 @@
+<?php
+
+namespace App\Enum;
+
+/**
+ * How a single-choice question is rendered: a radio list or a select.
+ */
+enum ChoiceWidget: string
+{
+    case RADIO = 'radio';
+    case DROPDOWN = 'dropdown';
+}