Could these "gently worn" jeans soon be yours?Calm down, everyone. It's a double entendre. Jennifer Siebel Newsom, erstwhile movie star and wife of our gubernatorial candidate and erstwhile mayor, will be "walking the jean carpet" noon today at 525 Castro as a celebrity guest of a "jeans exchange" benefiting Goodwill. It's conceivable our first lady will bring a few pairs to further the cause -- hence our headline. If it is not clearly denoted upon your calendar, today is "Levi's 501 Day" -- cle