Ship Windows MSIs and macOS disk images for the launcher

[its-janghoon]

Redrob Launcher installs Windows apps from an MSI and macOS apps from a DMG with a signed .app; the engine shipped neither, so the launcher's engine Install / auto-update worked on Linux only.

• installer/windows/redrob-code.wxs (WiX v5, per user, %LOCALAPPDATA%\Redrob\bin, redrob.exe + redrob-code.exe, PATH; same install as the Inno setup). sign-windows builds x64 + arm64 MSIs after the binaries are signed and signs them with the shared action alongside setup.exe.
• installer/macos/make-dmg.sh wraps the signed binary in Redrob Code.app (ai.redrob.code, version), signs the bundle, hdiutil DMG. sign-macos notarizes + staples redrob-code--macos-{aarch64,x86_64}.dmg.
• Attestation covers the new files. Asset names follow the launcher's ---..

Verification: release dry run before the next engine release (per Janghoon: build/test once, right before release).