feat(native): Tier B — WinRT rich toasts (P5-41/35) + Focus Assist sync (P5-56)

- toast.rs: Windows.UI.Notifications rich toast (reply input + Send action);
  in-process Activated event → emit lotus-notification-activate {path} (click) /
  lotus-notification-reply {roomId,text}. Falls back to tauri-plugin-notification
  (WinRT error / non-Windows). The NOTIFICATION_BRIDGE now routes notifications
  carrying a roomId (tag) to show_rich_toast. Features: UI_Notifications,
  Data_Xml_Dom, Foundation_Collections.
- focus_assist.rs: SHQueryUserNotificationState poll thread → emit
  focus-assist-changed {active} on QUNS_QUIET_TIME/PRESENTATION/D3D_FULLSCREEN/BUSY.
  No new Cargo features.

CI Windows compile pending (no local Rust toolchain). Runtime caveat: WinRT toasts
need a Start-menu shortcut + matching AppUserModelID (org.lotusguild.lotus-chat);
without it CreateToastNotifier errors and the code falls back to the plugin.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src-tauri/src/native/mod.rs

@@ -9,11 +9,13 @@
 use tauri::{AppHandle, Manager};
 
 pub mod chrome;
+pub mod focus_assist;
 pub mod jumplist;
 pub mod network;
 pub mod power;
 pub mod smtc;
 pub mod thumbbar;
+pub mod toast;
 
 /// Dispatch a DOM `CustomEvent` to the web client (mirrors `forward_deeplink` in
 /// lib.rs) so native modules can push data to the frontend without pulling in
@@ -35,5 +37,6 @@ pub fn setup(app: &AppHandle) -> tauri::Result<()> {
     thumbbar::setup(app)?;
     smtc::setup(app)?;
     network::setup(app)?;
+    focus_assist::setup(app)?;
     Ok(())
 }