Add timefix and vacation routes to backend; update frontend for new routes and page titles

backend/add-vacation-index.sql

@@ -0,0 +1,9 @@
+-- Füge Index für vacation Tabelle hinzu
+-- Optimiert die Abfrage: WHERE user_id = ? AND first_day >= ? ORDER BY first_day DESC
+
+CREATE INDEX idx_vacation_user_first_day 
+ON vacation (user_id, first_day DESC);
+
+-- Prüfe ob der Index erstellt wurde
+SHOW INDEX FROM vacation WHERE Key_name = 'idx_vacation_user_first_day';
+