feat: Add desktop scaling and fix linux postinst (#1800)

* fix: resolve Linux window close handler to prevent app hang

- Add delete-event callback that properly quits the application when window is closed

* feat: Add desktop scaling and fix linux postinst

- Implement desktop interface scaling in main.dart using FittedBox.
- Add desktop scaling setting UI.
- Add desktopScale to storage preference.
- Fix typos and logic in Linux postinst script.
- Update piliplus.desktop with StartupWMClass.

* update

Signed-off-by: dom <githubaccount56556@proton.me>

---------

Signed-off-by: Shao Guohao <shao.gh.98@gmail.com>
Co-authored-by: dom <githubaccount56556@proton.me>

lib/utils/storage_key.dart

@@ -152,7 +152,8 @@ abstract final class SettingBoxKey {
       isWindowMaximized = 'isWindowMaximized',
       showWindowTitleBar = 'showWindowTitleBar',
       desktopVolume = 'desktopVolume',
-      showTrayIcon = 'showTrayIcon';
+      showTrayIcon = 'showTrayIcon',
+      uiScale = 'uiScale';
 
   static const String subtitlePreferenceV2 = 'subtitlePreferenceV2',
       enableDragSubtitle = 'enableDragSubtitle',