fix: handle pre-parsed JSON data in email processor

The email_data column in PostgreSQL is a JSON type that auto-parses
the data, while SQLite stores it as a string. Updated the code to
check if email_data is already an object before attempting to parse.

This fixes the "Unexpected token o in JSON at position 1" error.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

backend/src/services/emailProcessor.js

@@ -350,7 +350,9 @@ async function processEmailQueue() {
     
     for (const email of pendingEmails) {
       try {
-        const emailData = JSON.parse(email.email_data || '{}');
+        const emailData = typeof email.email_data === 'string' 
+          ? JSON.parse(email.email_data || '{}')
+          : email.email_data || {};
         
         await sendTemplateEmail(
           email.recipient_email,