feat(前端): 实现用户登录、注册和搜索功能

- 新增登录和注册页面组件
- 实现用户登录、注册和登出逻辑
- 添加笔记搜索功能
- 更新主页组件，支持用户状态显示和搜索
- 引入 Pinia 状态管理库

biji-qianduan/src/router/index.js

@@ -1,6 +1,8 @@
 import { createRouter, createWebHistory } from 'vue-router';
 import HomePage from '../components/HomePage.vue';
 import MarkdownEditor from '../components/MarkdownEditor.vue';
+import LoginPage from '../components/LoginPage.vue';
+import RegisterPage from '../components/RegisterPage.vue';
 
 const routes = [
   {
@@ -22,6 +24,16 @@ const routes = [
     name: 'EditMarkdown',
     component: MarkdownEditor,
     props: true
+  },
+  {
+    path: '/login',
+    name: 'Login',
+    component: LoginPage
+  },
+  {
+    path: '/register',
+    name: 'Register',
+    component: RegisterPage
   }
 ];