fix(contact): 切换表单服务到 FormSubmit 并改进错误处理

- 将表单提交服务从 Formspree 切换到 FormSubmit（无需 API Key）
- 添加成功状态 URL 参数处理（?success=true）
- 改进错误提示，区分开发环境和生产环境
- 添加 _next 参数支持成功后重定向
- 重构状态初始化避免 useEffect 中同步调用 setState

src/app/(marketing)/contact/page.tsx

@@ -1,6 +1,7 @@
 'use client';
 
 import { useState, useEffect, useRef } from 'react';
+import { useSearchParams } from 'next/navigation';
 import { z } from 'zod';
 import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
@@ -28,12 +29,18 @@ interface FormErrors {
 }
 
 export default function ContactPage() {
+  const searchParams = useSearchParams();
+  const isSuccessFromRedirect = searchParams.get('success') === 'true';
   const [isVisible, setIsVisible] = useState(false);
-  const [showToast, setShowToast] = useState(false);
-  const [toastMessage, setToastMessage] = useState('');
-  const [toastType, setToastType] = useState<'success' | 'error'>('success');
+  const [showToast, setShowToast] = useState(isSuccessFromRedirect);
+  const [toastMessage, setToastMessage] = useState(
+    isSuccessFromRedirect ? '表单提交成功！我们会尽快与您联系。' : ''
+  );
+  const [toastType, setToastType] = useState<'success' | 'error'>(
+    isSuccessFromRedirect ? 'success' : 'success'
+  );
   const [isSubmitting, setIsSubmitting] = useState(false);
-  const [isSubmitted, setIsSubmitted] = useState(false);
+  const [isSubmitted, setIsSubmitted] = useState(isSuccessFromRedirect);
   const [formData, setFormData] = useState<ContactFormData>({
     name: '',
     phone: '',
@@ -43,6 +50,7 @@ export default function ContactPage() {
   });
   const [errors, setErrors] = useState<FormErrors>({});
   const sectionRef = useRef<HTMLElement>(null);
+  const hasProcessedSuccess = useRef(isSuccessFromRedirect);
 
   useEffect(() => {
     requestAnimationFrame(() => {
@@ -50,6 +58,13 @@ export default function ContactPage() {
     });
   }, []);
 
+  useEffect(() => {
+    if (isSuccessFromRedirect && !hasProcessedSuccess.current) {
+      hasProcessedSuccess.current = true;
+      window.history.replaceState({}, '', '/contact');
+    }
+  }, [isSuccessFromRedirect]);
+
   const validateField = (field: keyof ContactFormData, value: string) => {
     try {
       contactFormSchema.shape[field].parse(value);
@@ -92,21 +107,41 @@ export default function ContactPage() {
 
     setIsSubmitting(true);
     try {
-      const response = await fetch('https://formspree.io/f/' + process.env.NEXT_PUBLIC_FORMSPREE_ID, {
+      const formEndpoint = `https://formsubmit.co/${COMPANY_INFO.email}`;
+      const formBody = new URLSearchParams();
+      formBody.append('name', formData.name);
+      formBody.append('phone', formData.phone);
+      formBody.append('email', formData.email);
+      formBody.append('subject', formData.subject);
+      formBody.append('message', formData.message);
+      formBody.append('_subject', `网站留言: ${formData.subject}`);
+      formBody.append('_captcha', 'false');
+      formBody.append('_template', 'table');
+      formBody.append('_next', `${window.location.origin}/contact?success=true`);
+      
+      const response = await fetch(formEndpoint, {
         method: 'POST',
-        headers: { 'Content-Type': 'application/json', 'Accept': 'application/json' },
-        body: JSON.stringify(formData),
+        headers: { 'Accept': 'application/json' },
+        body: formBody,
       });
       
-      if (response.ok) {
+      const data = await response.json();
+      
+      if (response.ok && data.success === 'true') {
         setIsSubmitted(true);
         setToastMessage('表单提交成功！我们会尽快与您联系。');
         setToastType('success');
         setShowToast(true);
         setFormData({ name: '', phone: '', email: '', subject: '', message: '' });
       } else {
-        setToastMessage('提交失败，请稍后重试或直接发送邮件联系我们。');
-        setToastType('error');
+        const errorMsg = data.message || '提交失败，请稍后重试或直接发送邮件联系我们。';
+        if (errorMsg.includes('HTML files') || errorMsg.includes('web server')) {
+          setToastMessage('表单服务需要在生产环境激活。部署后首次提交会发送确认邮件到 ' + COMPANY_INFO.email);
+          setToastType('error');
+        } else {
+          setToastMessage(errorMsg);
+          setToastType('error');
+        }
         setShowToast(true);
       }
     } catch {