Add Vocab Trainer feature with routing, database schema, and translations

- Introduced Vocab Trainer functionality, including new routes for managing languages and chapters.
- Implemented database schema for vocab-related tables to ensure data integrity.
- Updated navigation and UI components to include Vocab Trainer in the social network menu.
- Added translations for Vocab Trainer in both German and English locales, enhancing user accessibility.

backend/app.js

@@ -18,6 +18,7 @@ import taxiRouter from './routers/taxiRouter.js';
 import taxiMapRouter from './routers/taxiMapRouter.js';
 import taxiHighscoreRouter from './routers/taxiHighscoreRouter.js';
 import termineRouter from './routers/termineRouter.js';
+import vocabRouter from './routers/vocabRouter.js';
 import cors from 'cors';
 import './jobs/sessionCleanup.js';
 
@@ -69,6 +70,7 @@ app.use('/api/taxi/highscores', taxiHighscoreRouter);
 app.use('/images', express.static(path.join(__dirname, '../frontend/public/images')));
 app.use('/api/contact', contactRouter);
 app.use('/api/socialnetwork', socialnetworkRouter);
+app.use('/api/vocab', vocabRouter);
 app.use('/api/forum', forumRouter);
 app.use('/api/falukant', falukantRouter);
 app.use('/api/friendships', friendshipRouter);