Fractal Terrain (2D): Diamond-Square Heightmap Generator

This top-down 2D companion to the 3D Procedural Terrain sim swaps fBm value-noise for a different classic fractal algorithm: diamond-square midpoint displacement. Starting from four random corner heights, alternating diamond and square averaging-plus-random-offset passes subdivide the grid down to single cells, with the random offset shrinking each pass by a roughness-controlled factor so the landscape stays coherent at every scale. The finished heightmap is normalised and rendered directly from above with elevation-band biome colouring (deep sea through snow peaks), a height-gradient view, and a slope-shading view, plus adjustable grid detail, roughness and sea level and a seeded regenerate button so any landscape can be reproduced exactly.