feat(treatment): select treatment behaviour by practice domain, not by if-branch

Everything that differs between specialties as data is already stored as data.
What is left is behaviour — when a case opens, what happens once a session ends —
so it becomes a TreatmentWorkflow resolved through a tagged-service registry.
The booking path calls one collaborator and never names a specialty; adding
dentistry is a new class, not an edit to confirmation.

A clinic that has chosen no practice domain still gets working multi-session
courses: DefaultTreatmentWorkflow answers for null and for any code without a
dedicated implementation, keeping "unset means behave as today, not error".
LaserTreatmentWorkflow is deliberately empty beyond claiming `beauty` — it is the
seam where laser-specific behaviour will land without disturbing anyone else.

Session due dates are anchored to the previous session's actual finish, so a
patient who comes twenty days late shifts the rest of their course instead of
getting the next session while it can still do nothing. Only the next session is
recomputed; later ones keep their estimate because they are anchored to nothing
yet.

Attachment targets the first session without an appointment rather than the
first open one: a patient booking again mid-course was otherwise matched to the
session that already had a booking, and the second appointment went nowhere.

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

src/Treatment/Repository/TreatmentSessionRepository.php

@@ -47,6 +47,27 @@ class TreatmentSessionRepository extends ServiceEntityRepository
             ->getOneOrNullResult();
     }
 
+    /**
+     * اولین جلسه‌ای که هنوز نوبتی ندارد.
+     *
+     * جدا از {@see self::findNextOpen()} است چون آن جلسهٔ رزروشده را هم «باز» می‌داند:
+     * بیماری که وسط دوره نوبت دوم می‌گیرد باید به جلسهٔ **بعدی** بچسبد، نه به جلسه‌ای
+     * که همین حالا نوبت دارد.
+     */
+    public function findNextUnbooked(TreatmentCase $case): ?TreatmentSession
+    {
+        return $this->createQueryBuilder('s')
+            ->where('s.treatmentCase = :case')
+            ->andWhere('s.appointment IS NULL')
+            ->andWhere('s.status IN (:open)')
+            ->setParameter('case', $case)
+            ->setParameter('open', [TreatmentSession::STATUS_PLANNED, TreatmentSession::STATUS_NO_SHOW])
+            ->orderBy('s.sessionNumber', 'ASC')
+            ->setMaxResults(1)
+            ->getQuery()
+            ->getOneOrNullResult();
+    }
+
     /** جلسهٔ انجام‌شدهٔ قبلی — لنگرِ محاسبهٔ سررسید جلسهٔ بعد. */
     public function findLastFinishedBefore(TreatmentCase $case, int $sessionNumber): ?TreatmentSession
     {