Queen Elizabeth II, Britain’s longest-reigning monarch and a rock of stability across much of a turbulent century, died Thursday after 70 years on the throne. She was 96. The palace announced her death at Balmoral Castle, her summer residence in Scotland, where members of the royal family had rushed to her side after her health took a turn for the worse. A link to the almost-vanished generation that fought World War II, she was the only monarch most Britons have ever known. Her 73-year-old son Prince Charles automatically becomes king, though the coronation might not take place for months. It …