fix(build): lazy initialize Resend to prevent build failures

The real root cause of CI build failures was NOT Turbopack, but
Resend initialization at module level without API key.

Problem:
- Resend was initialized at module level: const resend = new Resend(process.env.RESEND_API_KEY)
- During build, Next.js collects page data and imports all modules
- If RESEND_API_KEY is not set, Resend throws error: 'Missing API key'
- This caused build to fail with 'Failed to collect page data for /api/contact'

Solution:
- Implement lazy initialization pattern for Resend
- Only initialize Resend when actually needed (when sending emails)
- Add proper error handling if API key is missing

Changes:
- src/app/api/contact/route.ts: Add getResend() function with lazy init
- src/app/(marketing)/contact/actions.ts: Add getResend() function with lazy init

This allows the build to succeed even without RESEND_API_KEY in CI,
while still requiring it at runtime when actually sending emails.

src/app/(marketing)/contact/actions.ts

@@ -3,9 +3,21 @@
 import { Resend } from 'resend';
 import { z } from 'zod';
 
-const resend = new Resend(process.env.RESEND_API_KEY);
 const companyEmail = process.env.COMPANY_EMAIL || 'contact@novalon.cn';
 
+let resend: Resend | null = null;
+
+function getResend(): Resend {
+  if (!resend) {
+    const apiKey = process.env.RESEND_API_KEY;
+    if (!apiKey) {
+      throw new Error('RESEND_API_KEY environment variable is not set');
+    }
+    resend = new Resend(apiKey);
+  }
+  return resend;
+}
+
 const contactFormSchema = z.object({
   name: z.string().min(2, '姓名至少需要2个字符'),
   phone: z.string().regex(/^1[3-9]\d{9}$/, '请输入有效的手机号码'),
@@ -244,7 +256,7 @@ export async function submitContactForm(
   `;
 
   try {
-    const { data: emailData, error } = await resend.emails.send({
+    const { data: emailData, error } = await getResend().emails.send({
       from: '睿新致远官网 <onboarding@resend.dev>',
       to: [companyEmail],
       subject: `📧 ${data.subject} - ${data.name}`,

src/app/api/contact/route.ts

@@ -3,9 +3,21 @@ import { Resend } from 'resend';
 import { z } from 'zod';
 import { SecurityMiddleware } from '@/lib/security/middleware';
 
-const resend = new Resend(process.env.RESEND_API_KEY);
 const companyEmail = process.env.COMPANY_EMAIL || 'contact@novalon.cn';
 
+let resend: Resend | null = null;
+
+function getResend(): Resend {
+  if (!resend) {
+    const apiKey = process.env.RESEND_API_KEY;
+    if (!apiKey) {
+      throw new Error('RESEND_API_KEY environment variable is not set');
+    }
+    resend = new Resend(apiKey);
+  }
+  return resend;
+}
+
 let securityMiddleware = new SecurityMiddleware();
 
 export function setSecurityMiddleware(middleware: SecurityMiddleware) {
@@ -108,7 +120,7 @@ export async function POST(request: NextRequest) {
       </html>
     `;
 
-    const result = await resend.emails.send({
+    const result = await getResend().emails.send({
       from: '睿新致远官网 <onboarding@resend.dev>',
       to: [companyEmail],
       subject: `${sanitizedData.subject} - ${sanitizedData.name}`,