feat: statements table with positive/negative words M2M

- Trilingual positive + negative sentences, status, auto-timestamps
- statement_positive_words + statement_negative_words junction tables
- /api/statements CRUD + link/unlink for both word relations

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/index.js

@@ -30,6 +30,7 @@ app.use('/api/categories', auth, require('./routes/categories'));
 app.use('/api/objects', auth, require('./routes/objects'));
 app.use('/api/pairs', auth, require('./routes/pairs'));
 app.use('/api/questions', auth, require('./routes/questions'));
+app.use('/api/statements', auth, require('./routes/statements'));
 
 // 404
 app.use((req, res) => {