By Emily Monaco Tipping is far from a global practice, just ask any shell-shocked server handling a six-top of visiting Europeans. In many other countries, service is folded right into the menu price, rendering any tips truly gratuitous gratuities. American servers, of course, have long made the better part of their wages at the mercy of the diner. But many S.F. restaurants shifted to another model: one in which a service surcharge is included in the bill, and no “tip” is required or, in some cases, even allowed. The heyday of that theoretically more fair-minded pricing structure, though, may …