Allow sorting Customers by Last Booking and Total Bookings#4900

In the Customers panel, the Name column can currently be sorted alphabetically, which is very useful.

It would be very helpful to also allow sorting by:

1. Last booking / Last reservation date
2. Total bookings / Total number of appointments

For clinics and appointment-based businesses, this would make it much easier to identify recently active clients, inactive clients, and the most recurrent patients/customers.

This would improve follow-up, reactivation campaigns, administrative review, and general customer management.