feat(treatment): open a treatment case with snapshotted areas and its sessions

Opening a case copies what must not move afterwards — the session count and the
list of body areas, each with its category name — because a treatment record is
a medical document and editing settings tomorrow must not rewrite what was done
yesterday. The areas are the leaf categories under the service's own category:
"توتال" contains bikini, leg and hand, and treatment happens on those three, not
on the grouping node above them. A category with no children is its own single
area, so "لیزر دست" gets one area rather than none.

Every session in the course is created up front so that "session 5 of 8" has
somewhere to live, but none of them is booked: creating eight real appointments
would lock eight months of slots for a patient who may not attend session three.

CategoryClosureResolver gains leaves(); the graph walk it already does is what
tells a leaf from a grouping node, so this belongs next to descendants() rather
than in a second traversal elsewhere.

TreatmentCase and TreatmentSession carry no money field, and must not: billing
lives on PatientSession, which is created when an appointment is confirmed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/Treatment/Repository/SessionAreaRecordRepository.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace App\Treatment\Repository;
+
+use App\Treatment\Entity\SessionAreaRecord;
+use Doctrine\Bundle\DoctrineBundle\Repository\ServiceEntityRepository;
+use Doctrine\Persistence\ManagerRegistry;
+
+/**
+ * @extends ServiceEntityRepository<SessionAreaRecord>
+ */
+class SessionAreaRecordRepository extends ServiceEntityRepository
+{
+    public function __construct(ManagerRegistry $registry)
+    {
+        parent::__construct($registry, SessionAreaRecord::class);
+    }
+
+    public function findByUuid(string $uuid): ?SessionAreaRecord
+    {
+        return $this->findOneBy(['uuid' => $uuid]);
+    }
+}