Add Phase 2 & 3: Web frontend with authentication and tracking features

- Initialize Next.js 14 web application with Material UI and TypeScript
- Implement authentication (login/register) with device fingerprint
- Create mobile-first responsive layout with app shell pattern
- Add tracking pages for feeding, sleep, and diaper changes
- Implement activity history with filtering
- Configure backend CORS for web frontend (port 3030)
- Update backend port to 3020, frontend to 3030
- Fix API response handling for auth endpoints

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

maternal-web/lib/api/client.ts

@@ -0,0 +1,66 @@
+import axios from 'axios';
+
+const API_BASE_URL = process.env.NEXT_PUBLIC_API_URL || 'http://localhost:3000';
+
+export const apiClient = axios.create({
+  baseURL: API_BASE_URL,
+  headers: {
+    'Content-Type': 'application/json',
+  },
+  withCredentials: true,
+});
+
+// Request interceptor to add auth token
+apiClient.interceptors.request.use(
+  (config) => {
+    const token = localStorage.getItem('accessToken');
+    if (token) {
+      config.headers.Authorization = `Bearer ${token}`;
+    }
+    return config;
+  },
+  (error) => {
+    return Promise.reject(error);
+  }
+);
+
+// Response interceptor to handle token refresh
+apiClient.interceptors.response.use(
+  (response) => response,
+  async (error) => {
+    const originalRequest = error.config;
+
+    // If error is 401 and we haven't tried to refresh yet
+    if (error.response?.status === 401 && !originalRequest._retry) {
+      originalRequest._retry = true;
+
+      try {
+        const refreshToken = localStorage.getItem('refreshToken');
+        if (!refreshToken) {
+          throw new Error('No refresh token');
+        }
+
+        const response = await axios.post(`${API_BASE_URL}/api/v1/auth/refresh`, {
+          refreshToken,
+        });
+
+        const { accessToken } = response.data;
+        localStorage.setItem('accessToken', accessToken);
+
+        // Retry original request with new token
+        originalRequest.headers.Authorization = `Bearer ${accessToken}`;
+        return apiClient(originalRequest);
+      } catch (refreshError) {
+        // Refresh failed, clear tokens and redirect to login
+        localStorage.removeItem('accessToken');
+        localStorage.removeItem('refreshToken');
+        window.location.href = '/login';
+        return Promise.reject(refreshError);
+      }
+    }
+
+    return Promise.reject(error);
+  }
+);
+
+export default apiClient;