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/screens/main_screen.dart

@@ -28,7 +28,7 @@ class _MainScreenState extends State<MainScreen> {
           Container(
             decoration: const BoxDecoration(
               image: DecorationImage(
-                image: AssetImage('assets/images/bg.jpg'),
+                image: AssetImage('assets/images/bg.jpg', package: 'ai_chat_assistant'),
                 fit: BoxFit.cover,
               ),
             ),

lib/screens/part_screen.dart

@@ -1,3 +1,4 @@
+import 'package:ai_chat_assistant/utils/assets_util.dart';
 import 'package:flutter/material.dart';
 import 'dart:ui';
 import '../widgets/chat_box.dart';
@@ -146,7 +147,8 @@ class _PartScreenState extends State<PartScreen> {
                                       icon: Image.asset(
                                         'assets/images/open_in_full.png',
                                         width: 24,
-                                        height: 24
+                                        height: 24,
+                                        package: 'ai_chat_assistant',
                                       ),
                                       onPressed: _openFullScreen,
                                       padding: EdgeInsets.zero,