feat: add single instance plugin to prevent multiple app instances

Integrates tauri_plugin_single_instance to ensure only one instance of the application
runs at a time. When attempting to launch a second instance, it will focus the existing
window instead.

src-tauri/src/lib.rs

@@ -237,7 +237,22 @@ async fn update_tray_menu(
 
 #[cfg_attr(mobile, tauri::mobile_entry_point)]
 pub fn run() {
-    let builder = tauri::Builder::default()
+    let mut builder = tauri::Builder::default();
+
+    #[cfg(any(target_os = "macos", target_os = "windows", target_os = "linux"))]
+    {
+        builder = builder.plugin(tauri_plugin_single_instance::init(
+            |app, _args, _cwd| {
+                if let Some(window) = app.get_webview_window("main") {
+                    let _ = window.unminimize();
+                    let _ = window.show();
+                    let _ = window.set_focus();
+                }
+            },
+        ));
+    }
+
+    let builder = builder
         // 拦截窗口关闭：仅隐藏窗口，保持进程与托盘常驻
         .on_window_event(|window, event| match event {
             tauri::WindowEvent::CloseRequested { api, .. } => {