Fix macOS quit: intercept applicationShouldTerminate: to allow real exit

GLFW's applicationShouldTerminate: converts all quit paths (Cmd+Q, dock,
menu bar) into window close requests and returns NSTerminateCancel, so our
close-to-hide intercept was hiding the window instead of letting the app exit.

Fix by implementing applicationShouldTerminate: in ReopenDelegate, setting a
darwinQuitting flag before forwarding to GLFW's delegate. The close intercept
checks this flag and calls Window.Close() instead of Hide() when quitting.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/app_delegate_other.go

@@ -6,3 +6,7 @@ import "fyne.io/fyne/v2"
 
 func installReopenHandler(w fyne.Window) {
 }
+
+func isRealQuit() bool {
+	return false
+}