Unionized journalists at The Washington Post said they would stage a 24-hour strike on Thursday to protest staff cuts and what they call management's failure to bargain in good faith in contract talks that have stretched on for 18 months. The planned one-day walkout comes weeks after William Lewis, former publisher of The Wall Street Journal, was named chief executive and publisher of the Post as the venerable Washington daily newspaper was projecting a year-end loss of $100 million. The Post is one of many news outlets struggling to devise a sustainable business model in the decades since the internet upended the economics of journalism and digital advertising rates plummeted.