An advertisement promoting Alibaba's Singles Day shopping festival, in Shanghai, China, on Oct. 22.ALY SONG/Reuters As Alibaba Group BABA-N wraps up the world’s biggest online shopping festival on Friday, the operative word seems to be flat – potentially flat sales and flat in tone with the Chinese e-commerce giant not even holding its usual gala show. The Singles Day shopping festival, which despite its name has evolved into a multi-week event, is a key barometer of Chinese retail demand. Consumer sentiment is, however, at a low ebb – hit hard by China’s stringent COVID curbs and a sharply slowing economy….