[阶段1.1-1.7] 实现完整的认证系统

后端实现:
- 创建 AuthService 包含密码加密、JWT 生成和验证
- 创建 authMiddleware 用于 API 路由保护
- 实现 auth 路由 (register, login, logout, /me)

前端实现:
- 创建 Login 页面 (登录/注册标签页)
- 创建 ProtectedRoute 组件用于路由保护
- 更新 App.tsx 集成路由保护
- 前端 API 客户端已包含认证方法和拦截器

验收标准已满足:
- 用户可以注册和登录
- JWT Token 正确生成和验证
- 受保护的路由需要有效 Token
- 未认证用户重定向到登录页面

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

client/src/App.tsx

@@ -1,6 +1,8 @@
 import React from 'react';
-import { BrowserRouter as Router, Routes, Route } from 'react-router-dom';
+import { BrowserRouter as Router, Routes, Route, Navigate } from 'react-router-dom';
 import Layout from './components/Layout';
+import ProtectedRoute from './components/ProtectedRoute';
+import Login from './pages/Login';
 import Dashboard from './pages/Dashboard';
 import DataSync from './pages/DataSync';
 import Analysis from './pages/Analysis';
@@ -10,15 +12,26 @@ import Settings from './pages/Settings';
 function App() {
   return (
     <Router>
-      <Layout>
-        <Routes>
-          <Route path="/" element={<Dashboard />} />
-          <Route path="/sync" element={<DataSync />} />
-          <Route path="/analysis" element={<Analysis />} />
-          <Route path="/recommendations" element={<Recommendations />} />
-          <Route path="/settings" element={<Settings />} />
-        </Routes>
-      </Layout>
+      <Routes>
+        <Route path="/login" element={<Login />} />
+
+        <Route
+          path="*"
+          element={
+            <ProtectedRoute>
+              <Layout>
+                <Routes>
+                  <Route path="/" element={<Dashboard />} />
+                  <Route path="/sync" element={<DataSync />} />
+                  <Route path="/analysis" element={<Analysis />} />
+                  <Route path="/recommendations" element={<Recommendations />} />
+                  <Route path="/settings" element={<Settings />} />
+                </Routes>
+              </Layout>
+            </ProtectedRoute>
+          }
+        />
+      </Routes>
     </Router>
   );
 }