Dismissing any SwiftUI sheet while a .navigationTransition(.zoom) is
registered traps inside UIKit's _UIZoomTransitionController on the Mac
presentation path (macOS 26.4.1, builds 259/261 crash reports). The
same code path is stable on iOS and iPadOS, so this is an Apple
framework bug on Mac that can only be avoided.
Gate both zoom-transition modifiers on a cached runtime check for
isMacCatalystApp / isiOSAppOnMac so the Mac build falls into the
existing no-op branch while iOS and iPadOS keep the zoom animation.
