PARIS — Nobody shapes a jacket like Yves Saint Laurent — or, for that matter, a day suit or full pants. His superb tailoring was very much in evidence in the spring collection he showed Monday. And so was one of his favorite looks, the city halter. It all had a refined chic that appeals to the most confident of women. Here, the soft striped halter and pants. For more on the Paris collections, see pages 6 to 10.