P6.2: left-click tray icon shows window via SetSystemTrayWindow

Calls desk.SetSystemTrayWindow(w) after SetSystemTrayMenu so a left-click
on the tray icon shows/focuses the window without opening the menu. The
explicit "Show" menu item is kept for right-click access.

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

src/ui/tray.go

@@ -46,6 +46,7 @@ func configureSystemTray(a fyne.App, w fyne.Window) {
 		quit,
 	)
 	desk.SetSystemTrayMenu(menu)
+	desk.SetSystemTrayWindow(w)
 	w.SetCloseIntercept(func() {
 		// Closing hides the window instead of quitting because scheduler tools are
 		// expected to keep working in the background. The explicit Quit tray item