Fix Accessibility Issues in a Form

The starter code has a signup form with three fields (name, email, password) that works visually but has multiple accessibility violations. Fix them without changing the form's visual appearance or behavior. Four issues to fix: (1) inputs use placeholders instead of <label> elements, add labels with matching for/id; (2) required fields lack aria-required="true"; (3) CSS removes focus outlines with no replacement, add visible focus styles; (4) the submit button is a <div>, replace it with <button type="submit">.