Fix Resend contact sync payload and support separate contacts key

.env.example

@@ -7,6 +7,9 @@
 # 3. Paste it below
 RESEND_API_KEY=re_your_api_key_here
 
+# Optional: use a separate key for Contacts/Segments if your main key is send-only
+RESEND_CONTACTS_API_KEY=
+
 # Email address that receives contact form submissions
 RESEND_TO=vbvwithnate@outlook.com