Refact/plugin removal leftovers (#15864)

* fix(flutter): dispose the settings PageController and order dispose() correctly

`dispose()` began with `super.dispose()`, so the mixin chain marked the State
defunct before the WidgetsBindingObserver registration and the periodic timer
were released. The `PageController` was never disposed at all: `Get.delete`
only runs `onDelete()` for a `GetLifeCycleBase`, and a plain `ChangeNotifier`
is not one, so every open/close of the Settings tab leaked one controller with
its listener still attached.

Also guard `switch2page` on the `Rx<SettingsTabKey>` registration it actually
reads rather than only the `PageController` — now that both are really
deleted, a partial teardown would throw into the catch and silently open the
wrong tab — and re-check `mounted` after the await in the `_videoConnTimer`
tick, which `Timer::cancel` cannot stop once the body has started.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

* refact: finish the plugin-framework removal sweep

#15854 removed the feature but stopped short of its leftovers:

- `Uninstall`, `Enable`, `Disable`, `Options` and `Please install plugins`
  were consumed only by the deleted `flutter/lib/plugin/**`; drop them from
  template.rs and the 50 locale files (250 dead entries). `Update` and
  `Install` stay, still used by desktop_home_page.dart.
- The server no longer sends `PrvOnFailedPlugin`, and the client no longer
  offers to install plugins when privacy mode fails to turn on.
- Drop the MSI `F_Client_Plugins` / `F_Server_Plugins` localization strings;
  no `.wxs` references them.
- `_DisplayMenu`'s constructor became a pure pass-through once `pluginItem`
  was removed, and the cfg inside `handle_input` repeats the one on the
  function itself.
- Normalize `src/lang/sl.rs` to 0644, the only executable file under src/.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

* fix(client): handle legacy privacy mode plugin failures

Signed-off-by: fufesou <linlong1266@gmail.com>

---------

Signed-off-by: fufesou <linlong1266@gmail.com>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
Co-authored-by: fufesou <linlong1266@gmail.com>

flutter/lib/desktop/pages/desktop_setting_page.dart

@@ -90,7 +90,8 @@ class DesktopSettingPage extends StatefulWidget {
       if (index == -1) {
         return;
       }
-      if (Get.isRegistered<PageController>(tag: _kSettingPageControllerTag)) {
+      if (Get.isRegistered<PageController>(tag: _kSettingPageControllerTag) &&
+          Get.isRegistered<Rx<SettingsTabKey>>(tag: _kSettingPageTabKeyTag)) {
         DesktopTabPage.onAddSetting(initialPage: page);
         PageController controller =
             Get.find<PageController>(tag: _kSettingPageControllerTag);
@@ -158,17 +159,23 @@ class _DesktopSettingPageState extends State<DesktopSettingPage>
       if (!mounted) {
         return;
       }
-      _canBeBlocked.value = await canBeBlocked();
+      final blocked = await canBeBlocked();
+      if (!mounted) {
+        return;
+      }
+      _canBeBlocked.value = blocked;
     });
   }
 
   @override
   void dispose() {
-    super.dispose();
+    _videoConnTimer?.cancel();
+    WidgetsBinding.instance.removeObserver(this);
     Get.delete<PageController>(tag: _kSettingPageControllerTag);
     Get.delete<Rx<SettingsTabKey>>(tag: _kSettingPageTabKeyTag);
-    WidgetsBinding.instance.removeObserver(this);
-    _videoConnTimer?.cancel();
+    // Get.delete does not dispose a plain ChangeNotifier.
+    controller.dispose();
+    super.dispose();
   }
 
   List<_TabInfo> _settingTabs() {

flutter/lib/desktop/widgets/remote_toolbar.dart

@@ -1476,13 +1476,11 @@ class _DisplayMenu extends StatefulWidget {
   final FFI ffi;
   final ToolbarState state;
   final Function(bool) setFullscreen;
-  _DisplayMenu(
-      {Key? key,
-      required this.id,
+  const _DisplayMenu(
+      {required this.id,
       required this.ffi,
       required this.state,
-      required this.setFullscreen})
-      : super(key: key);
+      required this.setFullscreen});
 
   @override
   State<_DisplayMenu> createState() => _DisplayMenuState();