Build a playable Minecraft-style voxel sandbox in the browser (Three.js, single page, no external assets). Procedurally generated terrain with grass, dirt, stone, sand, water and trees; first-person WASD + mouse look, jump, break and place blocks with a hotbar of 6 block types; day/night cycle with a sun and moon; simple ambient occlusion so it looks good. It should be fun the moment it loads.