fix: 修复assets在example app中不能使用的问题 & 加入maven local的链接，修复flutter无法打包 aar的问题

lib/utils/assets_util.dart

@@ -0,0 +1,31 @@
+// assets_util.dart
+import 'package:flutter/widgets.dart';
+import 'package:flutter/foundation.dart';
+
+/**
+ * AssetsUtil
+ * @description: 资源工具类
+ * @author guangfei.zhao
+ */
+class AssetsUtil {
+
+  static const String packageName = 'ai_chat_assistant';
+
+  static AssetImage getImage(String imageName) {
+    return AssetImage(
+      'assets/images/$imageName',
+      package: packageName,
+    );
+  }
+
+  static Widget getImageWidget(String imageName, {BoxFit? fit, double? width, double? height}) {
+    return Image.asset(
+      'assets/images/$imageName',
+      package: packageName,
+      fit: fit,
+      width: width,
+      height: height,
+    );
+  }
+
+}