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>

src/server/connection.rs

@@ -1219,7 +1219,6 @@ impl Connection {
                     }
                 },
                 Err(err) => {
-                    #[cfg(not(any(target_os = "android", target_os = "ios")))]
                     if block_input_mode {
                         let _ = crate::platform::block_input(true);
                     }
@@ -5011,7 +5010,7 @@ impl Connection {
                         }
                     } else {
                         crate::common::make_privacy_mode_msg(
-                            back_notification::PrivacyModeState::PrvOnFailedPlugin,
+                            back_notification::PrivacyModeState::PrvOnFailed,
                             impl_key,
                         )
                     }