fix: Resolve Exchange email server self-signed certificate error

- Add TLS configuration to accept self-signed certificates
- Disable TLS/STARTTLS for port 25 when SMTP_SECURE=false
- Add ignoreTLS option for Exchange servers on port 25
- Update .env.example with Exchange-specific configuration
- Create comprehensive EMAIL_CONFIGURATION.md guide
- Support both Exchange internal servers and modern SMTP servers

This fixes the "self-signed certificate" error when connecting
to Microsoft Exchange servers on port 25 without TLS.

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

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

backend/src/services/report.service.js

@@ -27,6 +27,15 @@ class ReportService {
         user: config.email.auth.user,
         pass: config.email.auth.pass,
       },
+      // For Exchange Server on port 25 without TLS
+      tls: {
+        rejectUnauthorized: false, // Accept self-signed certificates
+        // If you want to disable TLS completely when secure is false:
+        ...(config.email.port === 25 && !config.email.secure ? { enabled: false } : {})
+      },
+      // Disable STARTTLS for port 25 if not using secure
+      requireTLS: config.email.secure,
+      ignoreTLS: config.email.port === 25 && !config.email.secure,
     });
 
     // Verify connection