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>

docs/api/practice-domain.md

@@ -31,12 +31,18 @@ be able to switch them back on.
             "code": "beauty",
             "name": "کلینیک زیبایی",
             "sort_order": 0,
-            "active": true
+            "active": true,
+            "has_workflow": true
         }
     ]
 }
 ```
 
+`has_workflow` می‌گوید آیا پیاده‌سازیِ `TreatmentWorkflow` مخصوصِ این کد ثبت شده یا حوزه
+فقط رفتار پیش‌فرض می‌گیرد. حوزهٔ بی‌workflow کار می‌کند — دوره‌های چندجلسه‌ای‌اش باز
+می‌شوند — ولی رفتار اختصاصی ندارد، و پنل ادمین پلتفرم باید همین را نشان دهد نه اینکه
+مدیر حدس بزند.
+
 **Errors:**
 | Code | HTTP | توضیح |
 |------|------|-------|

docs/api/treatment.md

@@ -130,6 +130,49 @@ Real 422 responses:
 
 ---
 
+## Opening a case — what happens on confirm
+
+There is no endpoint that opens a treatment case; it happens as a side effect of confirming an
+appointment, in `AppointmentConfirmationService::onConfirmed`:
+
+```
+نوبت تأیید شد
+  → PatientSession ساخته می‌شود (مالی، مثل همیشه)
+  → اگر سرویسِ نوبت پروتکل فعال دارد:
+       TreatmentWorkflowRegistry::for(clinic.practice_domain.code)->openCase(...)
+```
+
+The booking core never names a specialty. A `TreatmentWorkflow` is selected by the clinic's practice
+domain code through a tagged-service registry, so adding dentistry is a new class rather than a
+change in the booking path. `LaserTreatmentWorkflow` handles `beauty`;
+`DefaultTreatmentWorkflow` answers for everything else, including a clinic that has chosen no domain
+at all — `null` means "behave as today", never an error.
+
+What opening a case does:
+
+| | |
+|---|---|
+| پروندهٔ باز موجود | برگردانده می‌شود؛ پروندهٔ دوم برای همان بیمار و همان سرویس ساخته نمی‌شود |
+| نواحی | برگ‌های دستهٔ سرویس، با نامشان، در همان لحظه کپی می‌شوند |
+| جلسات | همهٔ گام‌های پروتکل ساخته می‌شوند، همه `planned` |
+| نوبت | به **اولین جلسهٔ بدون نوبت** می‌چسبد و آن جلسه `booked` می‌شود |
+| سررسید | جلسهٔ رزروشده ساعت نوبت را می‌گیرد؛ بقیه `null` می‌مانند |
+
+Failure to open a case is logged and swallowed — the appointment is booked and possibly paid for, and
+losing that is worse than losing the case file, which can be rebuilt.
+
+### Session due dates
+
+`due_at` of session *n* is `finished_at` of session *n−1* plus that step's `offset_days`. Only the
+**next** session is recomputed when one finishes; sessions further out keep their earlier estimate,
+because a number that is not yet anchored to anything real does not get more accurate by being
+recalculated.
+
+A no-show does not burn the session: its status becomes `no_show`, its appointment link is cleared,
+`total_sessions` is untouched, and the same session comes back to the front of the booking queue.
+
+---
+
 ## DELETE `/api/v1/service-item/{uuid}/treatment-protocol`
 
 Turn the switch off — the protocol, its steps and its staff list are removed and the service is