Kate Spade did $1.07B last year, down 10%, and its parent company just guided the brand to lose money next year. This ad is the rescue mission. The playbook is copied straight from its sister brand. Coach was the dated mall brand until Tapestry rebuilt it around one bag, the Tabby, priced under $500 and handed to Gen Z faces. It worked better than anyone expected. Coach grew 24% last year to $6.9B, now makes up 87% of Tapestry's sales, and of the 11 million new customers the company added, 35%…