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 |
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