add asset validation

lib/utils/asset_validator.dart

@@ -0,0 +1,15 @@
+import 'package:flutter/services.dart';
+
+class AssetValidator {
+  static Future<bool> isValidAsset(String? assetPath) async {
+    if (assetPath == null || assetPath.isEmpty) {
+      return false;
+    }
+    try {
+      await rootBundle.load(assetPath);
+      return true;
+    } catch (_) {
+      return false;
+    }
+  }
+}