CartoKit: Finalizing Procedural Island Generation

This final installment details how CartoKit bakes generated island data into a compact mesh, visualizes it with an egui viewer, and exports assets for other tools. It features three key components: a baked terrain mesh containing elevation, moisture, biome, and river metadata; a CPU debug renderer and viewer for visualizing the data; and export helpers for GLB, PNG, and GIF output. The entire process is efficient and modular, laying a solid foundation for future extensions.