LATHER IT UP, LACMA-STYLE: "Pure Beauty," the mega John Baldessari exhibit, is on now at the Los Angeles County Museum of Art. If you're expecting to find the usual postcards waiting in the gift shop at the end of the exhibit, you will, but you'll also find Pure Beauty soap. It's redolent -- love that word, have to use where/when we can -- of ginger and lavender. ART MEETS BODY: The soap is $15. And it will surely, we'll say with some confidence, be the first based-on-the-exhibit soap most people will ever buy. Love firsts.