fix(windows): merge taskbar icon (AUMID) + focus window on notification click

Taskbar showed two icons because the AppUserModelID was (a) set too late — after
the main window was built, so its taskbar button grouped under a mismatched
implicit AUMID — and (b) valued 'LotusGuild.LotusChat', which differs from the
bundle identifier 'org.lotusguild.lotus-chat' that Tauri's NSIS installer stamps
on its shortcuts. Fix both: set the AUMID at the top of run() before the window
is built (new set_process_aumid, split out of ensure_app_user_model_id), and
align the constant to the bundle identifier so the running window and a pinned
installer shortcut group together.

Notification click didn't raise the window: add a focus_main_window command
(reuses show_main) for the web/service-worker path, and call show_main directly
in the rich-toast Activated body-click handler.

Note: existing users who pinned the old mis-grouped icon may need to re-pin once.

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

src-tauri/src/lib.rs

@@ -466,7 +466,20 @@ fn flash_window(window: tauri::Window) -> Result<(), String> {
         .map_err(|e| e.to_string())
 }
 
+/// Bring the main window to the foreground. Invoked from the web side when a
+/// notification is clicked — the service-worker/page path can't raise the native
+/// OS window on its own (a WebView2 `client.focus()` only focuses the document).
+#[tauri::command]
+fn focus_main_window(app: tauri::AppHandle) {
+    show_main(&app);
+}
+
 pub fn run() {
+    // Advertise the process AUMID BEFORE the main window is built (in `.setup`,
+    // below) so the window's taskbar button groups under the same identity as the
+    // pinned installer shortcut. Must precede the WebviewWindowBuilder.
+    native::aumid::set_process_aumid();
+
     let port: u16 = 44548;
     let context = tauri::generate_context!();
 
@@ -492,6 +505,7 @@ pub fn run() {
             set_tray_unread,
             get_tray_dnd,
             flash_window,
+            focus_main_window,
             send_notification,
             check_for_update,
             install_update,