feat(treatment): bind an appointment to a chosen session, and free it on cancel

Two holes in how a course's later appointments were made.

The link from the unbooked queue carried nothing — `/admin/appointments/new`
with no parameters — so the secretary retyped the patient and the service, and
which case the appointment joined was inferred from the service they happened to
pick. A patient with two open courses had no way to say which one they meant,
and picking the wrong service silently opened a third case. (The suggestion link
did pass slot_start and resource_uuid, but the create page never read either.)

POST /api/v1/my/appointment now takes an optional treatment_session_uuid.
SessionBookingLink validates it — same tenant, still unbooked, case open, same
patient — and reserves that session. Confirm-time attachment steps aside when
the appointment already holds a session. The booking form states in words which
session, which course and which patient it is about to book, read from a new
GET /api/v1/treatment-session/{uuid}.

Nothing ever detached a session from its appointment, so a cancelled booking
left the session `booked` forever, and since findNextUnbooked requires
"has no appointment", it could never return to the queue. Cancellation and
no-show now release it back to `planned`. A finished session is history and is
left alone.

The system still never books the next appointment by itself — it only suggests.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/Treatment/Controller/TreatmentCaseController.php

@@ -140,6 +140,28 @@ class TreatmentCaseController extends BaseController
         ));
     }
 
+    /**
+     * یک جلسه به‌تنهایی — برای فرمِ «ثبت نوبت این جلسه».
+     *
+     * فرم باید بگوید نوبت برای کدام دوره و کدام بیمار ثبت می‌شود؛ بیمارِ چنددوره‌ای
+     * بدون این، اتصال را به حدسِ سرویس می‌سپارد.
+     */
+    #[Route('/api/v1/treatment-session/{uuid}', name: 'treatment_session_show', methods: ['GET'])]
+    public function showSession(#[CurrentUser] User $user, string $uuid): JsonResponse
+    {
+        $session = $this->requireSession($user, $uuid);
+        $case    = $session->getTreatmentCase();
+
+        return $this->success($session->toArray() + [
+            'case_uuid'    => $case->getUuid(),
+            'service'      => ['uuid' => $case->getServiceItem()->getUuid(), 'name' => $case->getServiceItem()->getName()],
+            'patient'      => [
+                'record_uuid' => $case->getPatientRecord()->getUuid(),
+                'name'        => $case->getPatientRecord()->getUser()->getRealName(),
+            ],
+        ]);
+    }
+
     /**
      * اسلات‌های پیشنهادی برای این جلسه.
      *