Stand up build.sx (macos + ios/ios-sim targets, bundle id
co.swipelab.m3te, output sx-out/ios/M3te.app, assets dir) and a minimal
main.sx that brings up the platform (UIKit+Metal on iOS, SDL3+GL on
macOS) and renders a solid-clear frame. Add assets/ and goldens/
directories and a .gitignore for build artifacts.
Modeled on game/build.sx and game/main.sx; modules resolve from the
compiler binary with no -L flag.
