Keep subject when applying reply template to preserve email threading

Templates now only fill the message body, not the subject, so the
Re: [original subject] line stays intact for proper Gmail threading.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/AdminPage.tsx

@@ -2751,7 +2751,6 @@ export default function AdminPage({ content, onSave, onLogout }: Props) {
 
     setContactReplyDraft({
       ...contactReplyDraft,
-      subject: template.subject,
       message: template.message,
     })
     setContactReplyMsg(`Applied template: ${template.label}.`)