完善桌面壳托盘关闭行为

主窗口关闭在托盘可用时隐藏到托盘

托盘不可用时保持默认关闭避免窗口无法恢复

补充关闭策略检查测试和架构文档

apps/desktop-shell/scripts/check-config.mjs

@@ -143,6 +143,11 @@ const requiredMainSnippets = [
   'TRAY_MENU_QUIT',
   'show_main_window',
   'reload_main_window',
+  'register_desktop_window_close_events',
+  'resolve_desktop_window_close_action',
+  'WindowEvent::CloseRequested',
+  'api.prevent_close()',
+  'close_window.hide()',
   'desktop tray registration failed',
   '"appearance.getColorScheme"',
   '"app.lifecycle"',