Dive Bar and two sister nightlife venues are expected to open within three months on K Street, breathing new life into the struggling pedestrian mall well ahead of other developments. San Francisco nightclub operator George Karpaty's trio of nightlife venues has been seen as competition by some at a time when local businesses continue to struggle and even close. Karpaty said he was lured to Sacramento partly by the success of nearby venues such as Social Nightclub, Ella, Grange and the Citizen Hotel. But Karpaty said he's developed concepts — a "mermaid bar," a gourmet pizza restaurant with acrobatic pizza tossers and a high-end, over-30 dance club — to further develop K Street Mall into