Add multi-select support to pmshare panel (#1779)

* Add multi-select support to share panel

- Replace single selection index with per-user selected flag
- Allow sending to multiple selected users
- Add sending state to prevent multiple clicks
- Update default selection logic to mark first user as selected

* 简化代码逻辑

* update

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

---------

Signed-off-by: lesetong <oscarlbw@qq.com>
Co-authored-by: bggRGjQaUbCoE <githubaccount56556@proton.me>

lib/pages/setting/models/style_settings.dart

@@ -669,7 +669,7 @@ List<SettingsModel> get styleSettings => [
   ),
   NormalModel(
     onTap: (context, setState) async {
-      var result = await Get.toNamed('/fontSizeSetting');
+      final double? result = await Get.toNamed('/fontSizeSetting');
       if (result != null) {
         Get.put(ColorSelectController()).currentTextScale.value = result;
       }