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/Workflow/DefaultTreatmentWorkflow.php

@@ -69,9 +69,18 @@ class DefaultTreatmentWorkflow implements TreatmentWorkflow
         $this->em->flush();
     }
 
-    /** نوبت به اولین جلسهٔ بدونِ نوبت وصل می‌شود، نه لزوماً به جلسهٔ اول. */
+    /**
+     * نوبت به اولین جلسهٔ بدونِ نوبت وصل می‌شود، نه لزوماً به جلسهٔ اول.
+     *
+     * مگر اینکه منشی هنگام ثبت، جلسه را صریح انتخاب کرده باشد؛ آن‌وقت نوبت از قبل
+     * وصل است و حدسِ «اولین بدون نوبت» فقط جلسهٔ دیگری را اشتباهی رزرو می‌کند.
+     */
     protected function attachToNextOpenSession(TreatmentCase $case, Appointment $appointment): void
     {
+        if ($this->sessions->findOneBy(['appointment' => $appointment]) !== null) {
+            return;
+        }
+
         $session = $this->sessions->findNextUnbooked($case);
 
         if ($session === null) {