Fix window close: use RegisterHook to hide instead of destroy

RegisterHook + e.Cancel() prevents Wails from destroying the WebView
when the window is closed. The app now hides to the system tray. Left-
click on the tray icon correctly restores the window.

cmd/desktop/main.go

@@ -23,6 +23,7 @@ import (
 	"time"
 
 	"github.com/wailsapp/wails/v3/pkg/application"
+	"github.com/wailsapp/wails/v3/pkg/events"
 	"github.com/zalando/go-keyring"
 )
 
@@ -760,6 +761,12 @@ func main() {
 	} else {
 		window.Center()
 	}
+
+	window.RegisterHook(events.Common.WindowClosing, func(e *application.WindowEvent) {
+		window.Hide()
+		e.Cancel()
+	})
+
 	window.Show()
 
 	systemTray.AttachWindow(window)