feat: add getBaseUrl function for consistent base URL generation across routes

feat(calendar): display local timezone in calendar view
feat(i18n): add timezone label to German and English translations

server/routes/auth.js

@@ -9,7 +9,7 @@ import { rateLimit } from 'express-rate-limit';
 import { RedisStore } from 'rate-limit-redis';
 import { getDb } from '../config/database.js';
 import redis from '../config/redis.js';
-import { authenticateToken, generateToken } from '../middleware/auth.js';
+import { authenticateToken, generateToken, getBaseUrl } from '../middleware/auth.js';
 import { isMailerConfigured, sendVerificationEmail } from '../config/mailer.js';
 import { log } from '../config/logger.js';
 
@@ -189,7 +189,7 @@ router.post('/register', registerLimiter, async (req, res) => {
       }
 
       // Build verification URL
-      const baseUrl = process.env.APP_URL || `${req.protocol}://${req.get('host')}`;
+      const baseUrl = getBaseUrl(req);
       const verifyUrl = `${baseUrl}/verify-email?token=${verificationToken}`;
 
       // Load app name from branding settings
@@ -303,7 +303,7 @@ router.post('/resend-verification', resendVerificationLimiter, async (req, res)
       [verificationToken, expires, now, user.id]
     );
 
-    const baseUrl = process.env.APP_URL || `${req.protocol}://${req.get('host')}`;
+    const baseUrl = getBaseUrl(req);
     const verifyUrl = `${baseUrl}/verify-email?token=${verificationToken}`;
 
     const brandingSetting = await db.get("SELECT value FROM settings WHERE key = 'branding'");