Let a circle pass through the origin and its centre be the point of intersection of two mutually perpendicular lines \( x + (k-1)y + 3 = 0 \) and \( 2x + k^2 y - 4 = 0 \). If the line \( x - y + 2 = 0 \) intersects the circle at the points \( A \) and \( B \), then \( (AB)^2 \) is equal to:
