feat(frontend): 构建前端 MVP，实现完整 UI 框架与 mock 数据层

- 安装 zustand + react-router-dom 依赖
- 修复 Vite 代理配置，添加 /auth 路由转发
- 实现 API 封装层（client.ts 统一 fetch、auth.ts 真实调用）
- 实现 mock 数据层（mock.ts 模拟 WebSocket 管线进度）
- 实现 4 个 zustand stores（auth/project/task/generation）
- 实现 5 个组件（StyleSelector/PromptEditor/GenerateForm/ProgressBar/AssetPreview）
- 实现 5 个页面（Login/Register/Project/Generate/Result）
- 实现路由含 ProtectedRoute 守卫
- 添加暗色主题全局样式
- 更新前端文档与 API 文档

frontend/src/router/index.tsx

@@ -0,0 +1,45 @@
+import { createBrowserRouter, Navigate, Outlet } from 'react-router-dom'
+import { useAuthStore } from '../stores/auth'
+import LoginPage from '../pages/LoginPage'
+import RegisterPage from '../pages/RegisterPage'
+import ProjectPage from '../pages/ProjectPage'
+import GeneratePage from '../pages/GeneratePage'
+import ResultPage from '../pages/ResultPage'
+
+function ProtectedRoute() {
+  const isAuthenticated = useAuthStore(s => s.isAuthenticated)
+  if (!isAuthenticated) return <Navigate to="/login" replace />
+  return <Outlet />
+}
+
+export const router = createBrowserRouter([
+  {
+    path: '/login',
+    element: <LoginPage />,
+  },
+  {
+    path: '/register',
+    element: <RegisterPage />,
+  },
+  {
+    element: <ProtectedRoute />,
+    children: [
+      {
+        path: '/',
+        element: <Navigate to="/projects/proj-default" replace />,
+      },
+      {
+        path: '/projects/:projectId',
+        element: <ProjectPage />,
+      },
+      {
+        path: '/projects/:projectId/generate',
+        element: <GeneratePage />,
+      },
+      {
+        path: '/projects/:projectId/tasks/:taskId',
+        element: <ResultPage />,
+      },
+    ],
+  },
+])