Native BLEND import

Blender has been around for a while, and so obviously has .blend. And that makes life a little complex for long-time Blender users because as the app evolved, so did the format.

Blender's own file format stores project data: scenes, meshes, materials, cameras, lights, armatures, animation, compression, and version-specific structure. Convert3D now reads much of that directly in TypeScript, with fallback behavior for files outside the native parser's reach.