feat(appointment): book with patient data, TTL lock, atomic conflict

book() now accepts for_self plus patient_* fields: for_self fills the
patient from the paying user's profile, otherwise patient_name/mobile are
required (422 if missing) and the rest are stored. Every booking starts
pending with a 15-minute expires_at. Persisting goes through
bookAtomically (re-check inside a transaction) so two concurrent requests
for the same slot can't both win — the loser gets 409.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Appointment/Repository/AppointmentRepository.php

@@ -21,6 +21,24 @@ class AppointmentRepository extends ServiceEntityRepository
         return $this->findOneBy(['uuid' => $uuid]);
     }
 
+    /**
+     * Persist a booking atomically: re-check the slot inside a transaction so
+     * two concurrent requests for the same slot cannot both succeed.
+     *
+     * @throws SlotTakenException if the slot is taken when the transaction commits
+     */
+    public function bookAtomically(Appointment $appointment): void
+    {
+        $em = $this->getEntityManager();
+        $em->wrapInTransaction(function () use ($em, $appointment): void {
+            if ($this->isSlotTaken($appointment->getDoctor(), $appointment->getSlotStart(), $appointment->getSlotEnd())) {
+                throw new SlotTakenException();
+            }
+            $em->persist($appointment);
+            $em->flush();
+        });
+    }
+
     /** Check if a slot is already taken (confirmed or pending) */
     public function isSlotTaken(Doctor $doctor, int $slotStart, int $slotEnd, ?int $excludeId = null): bool
     {

src/Appointment/Repository/SlotTakenException.php

@@ -0,0 +1,7 @@
+<?php
+
+namespace App\Appointment\Repository;
+
+class SlotTakenException extends \RuntimeException
+{
+}