nx_decl_simple_scene.nx

nx_decl_simple_scene.nx -- second declarative #tag-style primitive. license_tier: ORIGINAL One substrate call composes random_environment + camera + lighting into a fully-specified "simple scene" struct. Equivalent of the TypeScript `#simple_scene <modifier>` directive. Validates that the #tag pattern COMPOSES: nx_decl_simple_scene calls nx_decl_random_environment for the env half, then adds camera + light defaults per modifier. Per S-class roadmap §A3 -- second slice toward the user's vision: "define something like #random_environment real and it generates with other things like size or other stuff"