feat(admin): default the booking staff from the service's protocol, and call it پرسنل

The staff field started empty even when the service's treatment protocol already
named who may perform it — a decision made once in the service settings and then
asked again on every booking. The modal now reads that protocol and preselects
its first staff member, but only until the user touches the field; otherwise a
manual choice would be wiped on the next service change. A protocol with no
staff leaves it empty and does not block submission.

Renames the four user-facing 'اپراتور' strings to 'پرسنل', matching the record
in /admin/staff that they all refer to. ResourcesPage keeps the word: there it
names a kind of bookable resource (doctor, operator, room, device), not a
ClinicStaff row.

Drops a test whose premise the default invalidated; the two new ones cover both
sides — protocol with staff sends staff_uuid, protocol without staff sends none.

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

assets/admin/components/TreatmentCaseEditModal.tsx

@@ -209,7 +209,7 @@ function EditForm({ detail, doctors, doctorsLoading, staff, staffLoading, onSave
       </div>
 
       <div className="field-block">
-        <label>اپراتور</label>
+        <label>پرسنل</label>
         {/* «در حال خواندن» با «تعریف نشده» یکی نیست؛ بدون این تفکیک، فهرستِ هنوز
             نیامده به‌صورت «پرسنلی ندارید» خوانده می‌شد. */}
         {staffLoading ? (