refactor: normalize date handling to Tehran timezone

- Updated date handling in BlogSeoFields and ScheduleSection to use Tehran timezone utilities for consistency.
- Introduced `toTehranClockTime`, `tehranWallClockToUnix`, and `todayIso` functions for accurate date representation.
- Modified various components to utilize these new utilities, ensuring that date strings are correctly formatted and timestamps are accurately converted.
- Enhanced API documentation to clarify the handling of date fields, emphasizing the importance of server-local midnight.
- Added tests to verify that date overrides and holidays maintain the correct day without shifting due to timezone discrepancies.

assets/admin/pages/AppointmentCreatePage.tsx

@@ -14,7 +14,7 @@ import { WalletChargeLink } from '../components/AppointmentActions';
 import { useDoctorBookingServices } from '../hooks/useDoctorBookingServices';
 import ServiceSlotPicker from '../components/appointments/ServiceSlotPicker';
 import { tehranWallClockToUnix, rialToToman, tomanToRial } from '../lib/utils';
-import { digitsOnly } from '../lib/utils';
+import { digitsOnly, todayIso } from '../lib/utils';
 
 /**
  * افزودن نوبت — صفحهٔ کامل (بازسازی `CreateTurn.jsx` طرح tauri). از همان endpointهای
@@ -43,7 +43,7 @@ export default function AppointmentCreatePage() {
   const dbUuid = useAuthStore(s => s.dbUuid);
   const isDoctor = primaryRole === 'doctor';
 
-  const today = new Date().toISOString().slice(0, 10);
+  const today = todayIso();
 
   // ── پزشک
   const [doctorUuid, setDoctorUuid] = useState(isDoctor && dbUuid ? dbUuid : (params.get('doctor') ?? ''));