Refactor code and improve internationalization support

- Updated import statements to remove invisible characters.
- Standardized comments to use a consistent hyphen format.
- Adjusted username validation error messages for consistency.
- Enhanced email sending functions to include language support.
- Added email internationalization configuration for dynamic translations.
- Updated calendar and federation routes to include language in user queries.
- Improved user feedback messages in German and English for clarity.

server/routes/rooms.js

@@ -1,4 +1,4 @@
-import { Router } from 'express';
+import { Router } from 'express';
 import crypto from 'crypto';
 import fs from 'fs';
 import path from 'path';
@@ -648,7 +648,7 @@ router.post('/:uid/presentation', authenticateToken, async (req, res) => {
     const room = await db.get('SELECT * FROM rooms WHERE uid = ? AND user_id = ?', [req.params.uid, req.user.id]);
     if (!room) return res.status(404).json({ error: 'Room not found or no permission' });
 
-    // M16: stream-level size limit – abort as soon as 50 MB is exceeded
+    // M16: stream-level size limit - abort as soon as 50 MB is exceeded
     const MAX_PRESENTATION_SIZE = 50 * 1024 * 1024;
     const buffer = await new Promise((resolve, reject) => {
       const chunks = [];