feat: add the booking domain layer

tests/Entity/BookingTest.php

@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Entity;
+
+use App\Entity\Booking;
+use App\Entity\Resource;
+use App\Entity\ResourceType;
+use App\Entity\User;
+use PHPUnit\Framework\TestCase;
+
+class BookingTest extends TestCase
+{
+    public function testTheDateIsNormalisedToMidnightSoTheUniqueConstraintCannotBeSidestepped(): void
+    {
+        $booking = new Booking(
+            new User('[email protected]', 'A'),
+            new Resource(ResourceType::DESK, 'D1'),
+            new \DateTimeImmutable('2026-09-13 14:37:11'),
+        );
+
+        self::assertSame('2026-09-13 00:00:00', $booking->getDate()->format('Y-m-d H:i:s'));
+    }
+}