feat: enhance security logging and ensure rate limit blocks are properly tracked

- Add comprehensive logging for rate limit blocks with full request details
  - IP address (with proper proxy detection), user agent, headers, timestamps
  - Rate limit info (current count, limit, remaining, reset time)
  - Separate tracking for auth vs general endpoints

- Enhance authentication failure logging
  - JWT validation failures with detailed error info
  - Admin auth attempts without token
  - Failed token validation with user context
  - All events include IP, path, method, user agent

- Improve Winston logger configuration for production
  - Add automatic log rotation (10MB errors, 50MB combined)
  - Create separate security.log for auth/rate limit events
  - Ensure logs directory exists automatically
  - Add structured JSON format for log aggregation
  - Support container logging with LOG_TO_CONSOLE env var

- Create comprehensive documentation
  - Security logging guide with examples
  - Monitoring recommendations
  - Configuration reference

- Add test script to verify logging functionality

All rate limit settings remain configurable via admin panel:
- Window duration, max requests, auth limits
- Skip authenticated requests option
- Public endpoints only option

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

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

backend/src/services/emailProcessor.js

@@ -109,8 +109,9 @@ async function getRecipientLanguage(email, eventId = null) {
 
 // Process email template with variables
 async function processTemplate(template, variables, language = 'en') {
-  // Import date formatter
+  // Import date formatter and text formatters
   const { formatDate } = require('../utils/dateFormatter');
+  const { formatWelcomeMessage } = require('../utils/formatters');
   
   // Get the appropriate language fields
   const subjectField = language === 'de' ? 'subject_de' : 'subject_en';
@@ -142,6 +143,11 @@ async function processTemplate(template, variables, language = 'en') {
   if (processedVariables.archive_date) {
     processedVariables.archive_date = await formatDate(processedVariables.archive_date, language);
   }
+  
+  // Format welcome message for HTML display (preserve line breaks)
+  if (processedVariables.welcome_message) {
+    processedVariables.welcome_message = formatWelcomeMessage(processedVariables.welcome_message);
+  }
 
   // Get branding settings for logo
   let logoUrl = '';