Current implementation: goal-based difficulty ladder
This build is closest to the 2048 family, but it is not a one-to-one copy of the classic browser version. Each mode has a fixed clear goal, the panel shows the next spawn tile, and higher difficulties slightly increase how often a 4 appears. Easy, Normal, and Hard stay on 4x4 for shorter runs, while Expert moves to 5x5 and asks for 2048.