Doctor Desktop

A Consultation/Telemedicine slot can be created or edited so that it is shorter than one appointment, so it can never hold a booking. Only duration > 0 and buffer >= 0 are validated; slot length is not compared to the appointment duration.

Steps to Reproduce:

1. Open OPD > My Schedule and select a doctor.
2. Click Add Slot (or click an existing block to edit it).
3. Set Type = Consultation (OPD), Start = 11:00 AM, End = 11:02 AM, Appointment Duration = 15 min.
4. Click Create Slot / Save changes.

Expected Result: Error such as "Slot must be at least as long as one appointment (15 min)"; the slot is not saved.

Actual Result: The slot is saved. The grid shows an 11:00–11:02 row labelled "OPD · 15 min slots" with no booked/total count (capacity is floor(2/15) = 0), and no appointment can ever be booked in it.

Notes:

• Backend: ValidateScheduleTypeRules in DoctorScheduleService.cs has no (end - start) >= duration (+ buffer) check.
• Frontend: Add Slot and Edit Slot dialogs in the OPD schedule page have no such check either.
• Related but different: #799 (end time before start time for non-consultation types).