feat: window activation with xdotool

lib/main.dart

@@ -19,8 +19,12 @@ void main() async {
           final result = await Process.run('ps', ['-p', pid.toString()]);
           
           if (result.exitCode == 0) {
-            // Process alive - just exit without trying to activate
+            // Process alive - try to focus existing window
-            print('Umbrix уже запущен');
+            try {
+              await Process.run('xdotool', ['search', '--name', 'Umbrix', 'windowactivate']);
+            } catch (_) {
+              // xdotool not available, just exit
+            }
             exit(0);
           } else {
             // Stale lock - remove it