Location availability now also blocks double coach scheduling

Location availability has been expanded so that coaches can no longer accidentally create an event at a location that is already occupied at that moment. If a class, appointment, or other calendar item is already scheduled at a location, that location is blocked for that time.

For clients, this availability was already checked during the booking process, but this check now also applies on the coach's side when creating or scheduling events. This prevents locations from being double-booked and keeps the calendar more reliable for both coaches and clients.

This makes planning lessons, appointments, and location-specific activities clearer and prevents confusion regarding double occupancy of rooms or training locations.