Store the birthday as a plain TT.MM.JJJJ text field in the backend

The field was declared as a Contao date field, so DC_Table parsed the
stored W&K format with the website's date format and threw "Invalid
date" when opening a booking. A save callback now normalises and
validates the value the same way the frontend form does.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

contao/dca/tl_wk_booking.php

@@ -188,7 +188,8 @@ $GLOBALS['TL_DCA']['tl_wk_booking'] = [
         'birthday' => [
             'exclude' => true,
             'inputType' => 'text',
-            'eval' => ['rgxp' => 'date', 'maxlength' => 10, 'tl_class' => 'w50'],
+            // Wird wie im Formular als TT.MM.JJJJ gespeichert (W&K-Format), siehe BirthdayListener
+            'eval' => ['maxlength' => 10, 'placeholder' => 'TT.MM.JJJJ', 'tl_class' => 'w50'],
             'sql' => ['type' => 'string', 'length' => 10, 'default' => ''],
         ],
         'teacherPosition' => [

src/EventListener/DataContainer/BirthdayListener.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Mummert\ContaoWkSyncBundle\EventListener\DataContainer;
+
+use Contao\CoreBundle\DependencyInjection\Attribute\AsCallback;
+use Mummert\ContaoWkSyncBundle\Booking\BookingCreator;
+
+/**
+ * Der Geburtstag wird wie im Anmeldeformular als TT.MM.JJJJ gespeichert (W&K-Format), unabhängig vom
+ * Datumsformat der Website. Ein Contao-Datumsfeld (rgxp=date) würde den gespeicherten Wert mit dem
+ * Systemformat parsen und im Backend einen Fehler werfen.
+ */
+#[AsCallback(table: 'tl_wk_booking', target: 'fields.birthday.save')]
+class BirthdayListener
+{
+    public function __invoke(mixed $value): string
+    {
+        $value = trim((string) $value);
+
+        if ('' === $value) {
+            return '';
+        }
+
+        $normalized = BookingCreator::normalizeDate($value);
+
+        if (!preg_match('/^(\d{2})\.(\d{2})\.(\d{4})$/', $normalized, $m) || !checkdate((int) $m[2], (int) $m[1], (int) $m[3])) {
+            throw new \RuntimeException(\sprintf($GLOBALS['TL_LANG']['ERR']['date'] ?? 'Ungültiges Datum "%s"', $value));
+        }
+
+        return $normalized;
+    }
+}