Add dotenv package for environment variable management and refactor SMTP credential handling in email services. Enhance error handling for missing SMTP credentials across various API endpoints to improve reliability and maintainability.

server/utils/email-service.js

@@ -80,13 +80,23 @@ function getEmailRecipients(data, config) {
  * @returns {Object} Nodemailer transporter
  */
 function createTransporter() {
+  const smtpUser = process.env.SMTP_USER
+  const smtpPass = process.env.SMTP_PASS
+  
+  if (!smtpUser || !smtpPass) {
+    throw new Error(
+      'SMTP-Credentials fehlen! Bitte setzen Sie SMTP_USER und SMTP_PASS in der .env Datei.\n' +
+      `Aktuell: SMTP_USER=${smtpUser ? 'gesetzt' : 'FEHLT'}, SMTP_PASS=${smtpPass ? 'gesetzt' : 'FEHLT'}`
+    )
+  }
+  
   return nodemailer.createTransporter({
     host: process.env.SMTP_HOST || 'localhost',
     port: parseInt(process.env.SMTP_PORT) || 587,
     secure: process.env.SMTP_SECURE === 'true',
     auth: {
-      user: process.env.SMTP_USER,
-      pass: process.env.SMTP_PASS
+      user: smtpUser,
+      pass: smtpPass
     }
   })
 }