WHEN Murray Lender talked about bagels, as he did all the time, he could wax philosophical. A bagel, he said, was a paradox. Shiny-brown and crispy on the outside; chewy and soft on the inside. Boiled, then baked. The personality was complex, since that hole-in-the-roll was never the same shape twice. But the sheer deliciousness was simple. He liked his warmed, though on TV ads he would demolish them toasted, the butter just melting, with an irresistible crunching sound. Close your eyes, munch a Lender's bagel, and you were as near as you could get to heaven without seeing the Pearly Gates.