feat: accept form submissions from the websites over an API endpoint

tests/Model/ApplicationFormSubmissionDtoTest.php

@@ -0,0 +1,56 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Model;
+
+use App\Model\ApplicationFormSubmissionDto;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * The normalization the json column relies on: no empty answers, numbers as strings, booleans
+ * kept, and a multi-select as a flat list of what was picked.
+ */
+class ApplicationFormSubmissionDtoTest extends TestCase
+{
+    public function testEmptyAnswersAreDropped(): void
+    {
+        $dto = $this->dto(['Nationalität' => 'deutsch', 'Führerschein' => '', 'Sprachen' => [], 'Sport' => null]);
+
+        $this->assertSame(['Nationalität' => 'deutsch'], $dto->getNormalizedDetails());
+    }
+
+    public function testNumbersBecomeStringsAndBooleansStay(): void
+    {
+        $dto = $this->dto(['Skifahrer seit' => 2004, 'Datenschutz' => true]);
+
+        $this->assertSame(['Skifahrer seit' => '2004', 'Datenschutz' => true], $dto->getNormalizedDetails());
+    }
+
+    public function testAMultiSelectStaysAFlatListOfLabels(): void
+    {
+        $dto = $this->dto(['Ich fahre' => ['Ski', 'Snowboard']]);
+
+        $this->assertSame(['Ich fahre' => ['Ski', 'Snowboard']], $dto->getNormalizedDetails());
+    }
+
+    public function testARelativeSubmissionTimeIsNotADate(): void
+    {
+        $this->assertNull((new ApplicationFormSubmissionDto(submittedAt: 'now'))->getSubmittedAt());
+        $this->assertNull((new ApplicationFormSubmissionDto(submittedAt: '2026-09-22'))->getSubmittedAt());
+        $this->assertNotNull((new ApplicationFormSubmissionDto(submittedAt: '2026-09-22T12:30:00+02:00'))->getSubmittedAt());
+    }
+
+    /**
+     * @param array<string, mixed> $details
+     */
+    private function dto(array $details): ApplicationFormSubmissionDto
+    {
+        return new ApplicationFormSubmissionDto(
+            form: 'applicationform',
+            formLabel: 'Bewerbungsformular',
+            submittedAt: '2026-09-22T12:30:00+02:00',
+            details: $details,
+        );
+    }
+}