WALNUT CREEK — Almost a month after an internal probe pushed 50 immigrant workers out of their jobs at a downtown Target store, interviews with former and current store employees portray a mass firing that was selective, planned in advance and confusing to many of those forced out. Sparked by an allegation that illegal immigrants worked on the night shift, the Walnut Creek store last month attracted the attention of the Minneapolis corporate headquarters of the 1,700-store chain. The company sent a team to investigate, according to several people close to the incident. By the end of the second week...