Canteen Management

The coupon print sheet (/coupons/[id]/print, barcoded cutouts per coupon) was fully built but unreachable from anywhere in the portal -- no link to it existed on the Coupons page itself, same zero-callers shape found earlier for MealSheetService. Found while explaining to the module owner how a real cashier would ever get an individual coupon code to scan -- the answer is this print sheet, which nobody could actually open. Added a Print icon button per book row, opens /coupons/{id}/print in a new tab, same pattern as the POS receipt print.