Share the base++zim++trailer assembly behind a small helper, then add two bundle
builders on top: BuildApp writes a macOS .app (Info.plist, the viewer under
Contents/MacOS, an .icns in Resources), and BuildAppDir writes an AppImage-style
.AppDir (AppRun, a Terminal=false .desktop launcher, a PNG icon). Both keep the
trailer at the tail so Embedded still finds the archive at runtime.
Duc-Tam Nguyen