fix(mobile): change update check interval to 90-300s random

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mobile-app/lib/features/home/presentation/pages/home_shell_page.dart

@@ -51,8 +51,8 @@ class _HomeShellPageState extends ConsumerState<HomeShellPage>
 
     // 如果从未检查过，或者已过冷却时间，则检查
     if (_nextCheckAllowedTime == null || now.isAfter(_nextCheckAllowedTime!)) {
-      // 设置下次允许检查时间（30-90秒随机间隔）
-      final randomSeconds = 30 + Random().nextInt(61); // 30 + 0~60 = 30~90
+      // 设置下次允许检查时间（90-300秒随机间隔）
+      final randomSeconds = 90 + Random().nextInt(211); // 90 + 0~210 = 90~300
       _nextCheckAllowedTime = now.add(Duration(seconds: randomSeconds));
       await checkForAppUpdate(context);
     }