完成私信界面，和侧边栏组件

Front/vue-unilife/src/components/MessageNav.vue

@@ -1,6 +1,6 @@
 <template>
     <div class="left-nav">
-      <div class="nav-title">消息中心</div>
+      <div class="nav-title">消息中心</div>
       <ul class="nav-list">
         <li 
           v-for="(item, index) in navItems" 
@@ -22,10 +22,10 @@
   const activeIndex = ref(0);
   
   const navItems = [
-    { text: '私信消息' },
-    { text: '评论回复' },
-    { text: '收到的赞' },
-    { text: '系统通知' }
+    { text: '通知消息' },
+    { text: '系统通知' },
+    { text: '用户消息' },
+    { text: '系统消息' }
   ];
   
   const handleNavClick = (index: number) => {