fix: improve email processor reliability and add diagnostic tools

- Enhanced email processor with comprehensive logging
- Added error handling for database queries in email processing
- Fixed duplicate export in module.exports
- Added testEmailConnection() function for connectivity testing
- Created diagnostic scripts:
  - check-email-processor.js: Full diagnostic with manual processing
  - run-email-processor.js: Standalone processor (can run once or continuously)
  - check-email-environment.js: Environment and configuration checker
- Fixed missing translation: added 'common.unknown' in EN/DE locales

This should help identify why emails aren't being processed on production.

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

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

backend/src/services/emailProcessor.js

@@ -325,6 +325,8 @@ async function sendTemplateEmail(to, templateKey, variables) {
 
 // Process email queue
 async function processEmailQueue() {
+  logger.info('Email queue processor: Checking for pending emails...');
+  
   try {
     // Try to initialize transporter if it's null (in case it failed at startup)
     if (!transporter) {
@@ -336,13 +338,20 @@ async function processEmailQueue() {
       }
     }
     
-    const pendingEmails = await db('email_queue')
-      .where('status', 'pending')
-      .where('retry_count', '<', 3)
-      .orderBy('created_at', 'asc')
-      .limit(10);
+    let pendingEmails = [];
+    try {
+      pendingEmails = await db('email_queue')
+        .where('status', 'pending')
+        .where('retry_count', '<', 3)
+        .orderBy('created_at', 'asc')
+        .limit(10);
+    } catch (dbError) {
+      logger.error('Failed to query email queue:', dbError);
+      return;
+    }
     
     if (pendingEmails.length === 0) {
+      logger.info('Email queue processor: No pending emails found');
       return;
     }
 
@@ -418,17 +427,45 @@ async function queueEmail(eventId, recipientEmail, emailType, emailData) {
   }
 }
 
+// Test email connection
+async function testEmailConnection() {
+  try {
+    if (!transporter) {
+      await initializeTransporter();
+    }
+    if (!transporter) {
+      return false;
+    }
+    await transporter.verify();
+    return true;
+  } catch (error) {
+    logger.error('Email connection test failed:', error);
+    return false;
+  }
+}
+
 // Start email queue processor
 let emailQueueInterval = null;
 
 function startEmailQueueProcessor() {
+  logger.info('Email queue processor: Attempting to start...');
+  
   if (!emailQueueInterval) {
     // Process immediately on start
-    processEmailQueue();
+    processEmailQueue().catch(err => {
+      logger.error('Email queue processor: Initial processing failed:', err);
+    });
     
     // Then process every minute
-    emailQueueInterval = setInterval(processEmailQueue, 60000);
-    logger.info('Email queue processor started');
+    emailQueueInterval = setInterval(() => {
+      processEmailQueue().catch(err => {
+        logger.error('Email queue processor: Periodic processing failed:', err);
+      });
+    }, 60000);
+    
+    logger.info('Email queue processor started successfully');
+  } else {
+    logger.info('Email queue processor: Already running');
   }
 }
 
@@ -452,6 +489,6 @@ module.exports = {
   sendTemplateEmail,
   processEmailQueue,
   queueEmail,
-  startEmailQueueProcessor,
-  stopEmailQueueProcessor
+  stopEmailQueueProcessor,
+  testEmailConnection
 };