Add Compare with Resend panel to Subscribers; stop resubscribing opted-out contacts; v2.6.1

- Subscribers: compare in-app list with Resend audience/segment, with one-click fixes
- syncContactToResend no longer resets unsubscribed on existing contacts

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

server/email.js

@@ -89,17 +89,22 @@ export async function syncContactToResend(name, email) {
   const { firstName, lastName } = splitName(name)
   const contactResend = new Resend(process.env.RESEND_CONTACTS_API_KEY ?? process.env.RESEND_API_KEY)
   try {
-    const { error: contactError } = await contactResend.contacts.create({
+    // Never touch `unsubscribed` for a contact that already exists — otherwise a form submission
+    // would silently resubscribe someone who opted out in Resend.
+    const { data: existing } = await contactResend.contacts.get({ email })
+    if (existing) {
+      const { error: updateError } = await contactResend.contacts.update({ email, firstName, lastName })
+      if (updateError) console.error('[resend] contact sync error:', updateError)
+      return
+    }
+    const { error: createError } = await contactResend.contacts.create({
       email,
       firstName,
       lastName,
       unsubscribed: false,
       ...(process.env.RESEND_SEGMENT_ID ? { segments: [{ id: process.env.RESEND_SEGMENT_ID }] } : {}),
     })
-    if (contactError) {
-      const { error: updateError } = await contactResend.contacts.update({ email, firstName, lastName, unsubscribed: false })
-      if (updateError) console.error('[resend] contact sync error:', updateError)
-    }
+    if (createError) console.error('[resend] contact sync error:', createError)
   } catch (err) {
     console.error('[resend] contact sync exception:', err)
   }