联系表单

Create a contact form with name, email, and message fields. Include client-side validation: all fields required, valid email format, and 500 character limit on message. Show inline error messages, a loading state on submit, and a success message after submission. Use shadcn/ui Input, Textarea, Button, and Label components and Tailwind CSS. Make it accessible with proper labels and focus states.

创建一个包含姓名、邮箱和留言字段的联系表单。包含客户端验证：所有字段必填、邮箱格式正确、留言限制 500 字符。显示内联错误信息、提交时加载状态和提交后的成功提示。使用 shadcn/ui Input、Textarea、Button 和 Label 组件以及 Tailwind CSS。确保可访问性，包含正确标签和聚焦状态。