Car production set records in China last year. Restaurants and hotels were increasingly full. Construction of new factories surged. Yet China’s economic strengths conceal weaknesses. Deep discounts helped drive car sales, particularly for electric cars. Diners and travelers chose cheaper dishes and less expensive hotels. Many factories ran at half capacity or less because of weak demand inside China, and are working to export more to make up for it. China’s economy grew 5.2 percent last year as it rebounded from nearly three years of stringent “zero Covid” pandemic control…