Studio: macOS cross-platform build (CLI + Studio + release)

Goal

Follow-up to #119 (closed) (closed). Bring the macOS Studio + CLI to the same state Windows now has: compiling, running, and shipping. #119 (closed) focused on Windows (primary market) and left macOS untouched — it still builds -Dcli-only in CI and the release matrix.

Current state

  • CLI cross-compiles for aarch64-macos (-Dcli-only) in CI/release.
  • The full Studio does not cross-compile from Linux: zig build -Dtarget=aarch64-macos -Dno-test fails with: error: '--sysroot' (or '-Dsystem_include_path'/'-Dsystem_framework_path'/'-Dlibrary_path') is required when building SDL for non-native macOS targets i.e. SDL3 needs the macOS SDK frameworks (Metal/Cocoa) to link.

Tasks

  • Provide a macOS SDK sysroot for cross-compiling SDL3 (or build natively on a macOS runner).
  • Get the full Studio compiling for aarch64-macos (and ideally x86_64-macos).
  • Verify GPU backend selection resolves to Metal (the Vulkan-first path in initBackend should fall back cleanly). Note the 3D viewport is SPIRV-only, so it will show "unavailable" on Metal until DXIL/MSL shaders exist (shared with the Windows viewport task).
  • Verify window creation + input on macOS (Apple Silicon; Intel if feasible).
  • Drop -Dcli-only from the macOS CI compile-check and release matrix once the Studio builds.
  • Update platform docs.

Acceptance

  • Studio compiles and runs on macOS (Apple Silicon).
  • CI compile-checks the full macOS Studio.
  • macOS release ships CLI + Studio.