Abstract Shape Hierarchy with Rectangle and Triangle

Create an abstract class Shape with an abstract method double area() and a concrete method String label() that returns "Shape". Then create two subclasses:

1. Rectangle — takes width and height. area() returns width * height. Override label() to return "Rectangle".
2. Triangle — takes base and height. area() returns 0.5 * base * height. Override label() to return "Triangle".

Do NOT write a main method.